Fuel composition and aging estimation

ABSTRACT

Methods and systems are provided for estimating ethanol content in fuel and an age of the fuel in a vehicle engine. In one example, a method may include estimating fuel ethanol content and/or fuel age based on fuel temperature, a speed of sound in fuel, and an attenuation co-efficient of an ultrasonic signal in fuel. One or more engine operating parameters may be adjusted based on the estimated fuel ethanol content and fuel age.

FIELD

The present description relates generally to methods and systems forestimating ethanol content in fuel and an age of the fuel in a vehicleengine.

BACKGROUND/SUMMARY

Flexible fuel vehicles (FFVs) are an alternative to conventionalgasoline-driven vehicles and include an internal combustion engine tocombust mixtures of gasoline and a secondary fuel, such as ethanol,methanol, propanol, or other alcohols and octane improvers. Fuel blendsincorporating ethanol are particularly popular due to a derivation ofethanol from biomass, with various feedstocks available fromagriculture. A flexible fuel engine may be adapted to burn fuel mixturesof 0-100% ethanol, thereby reducing the well-to-wheel carbon footprintcompared to gasoline. In hybrid vehicles, fuel may remain unused in thefuel tank as the vehicle may be propelled for prolonged periods solelyusing motor torque. Aging may cause changes in fuel composition. Forexample, to determine suitable air-fuel ratios at combustion chambers ofthe engine, the PCM may utilize an estimate or measurement of the fuelcomposition (e.g., percentage of ethanol) and an age of fuel todetermine an amount of fuel to be injected.

Various approaches are provided for estimating ethanol content in aflexible fuel. For example, in U.S. Pat. No. 7,523,723, Marriott et al.discloses a method for determining ethanol content in fuel based on fuelrail pressure characteristics. An effective bulk modulus of the fuel anda pressure perturbation signature may be determined from the fuel railpressure and fuel ethanol content may be estimated based on one or moreof the effective bulk modulus of the fuel and the pressure perturbationsignature.

However, the inventors herein have recognized potential disadvantageswith the above approach. As one example, Marriott et al. does notdisclose a method for determining age of fuel in the fuel tank. Ingasoline fuels, lighter and more volatile ends (molecules with fewerCarbon atoms e.g. C₃ and C₄) may evaporate leaving behind an agedgasoline fuel with higher concentration of heavier less volatile ends.In hybrid vehicles, fuel aging may be significant as the engine may notbe operated for prolonged durations. The concentration of the lighterand the heavier ends may affect a desired amount of fuel injected forcombustion. Further, an engine system may not include a fuel railpressure sensor which may be used to determine the fuel rail pressurecharacteristics.

The inventors herein have recognized that the issues described above maybe addressed by a method for an engine comprising: adjusting engineoperation based on an estimated fuel ethanol content and/or fuel age,the fuel ethanol content and/or fuel age estimated based on each of afuel temperature, a speed of sound in fuel, and an attenuationco-efficient of an ultrasonic signal in fuel. In this way, by monitoringfuel characteristics as estimated by existing sensors both fuel ethanolcontent and fuel aging may be estimated.

In one example, a fuel ethanol content measurement may be carried outimmediately after a refueling event and a fuel aging estimation may becarried out periodically. An ultrasonic signal generator coupled insidea fuel tank may be used to generate an ultrasonic signal that travelsthrough the fuel contained in the tank. A speed of sound in fuel may beestimated based on a time of travel of the ultrasonic signal through thefuel, back and forth between a first wall of the fuel tank and a second,opposite, wall of the fuel tank, and a distance between the first walland the second wall. Further, an attenuation co-efficient of theultrasonic signal may be estimated based on a change in amplitude of theultrasonic signal reaching the ultrasonic signal sensor after beingreflected from the second wall. In a flex-fuel vehicle, fuel ethanolcontent may be estimated as a function of each of a fuel temperature,the speed of sound in fuel, and the attenuation co-efficient in fuel. Ingasoline engines, fuel aging may also be estimated as a differentfunction of fuel temperature, the speed of sound in fuel, and theattenuation co-efficient in fuel. Based on the estimated fuel ethanolcontent and fuel age, engine operating parameters including spark timingand fuel injection amount may be adjusted. If the fuel age is higherthan a threshold, the operator may be notified to change the fuel in thefuel tank.

In this way, by using an ultrasonic signal generated by a signalgenerator located inside the fuel tank, accuracy of the fuel ethanolcontent and fuel age determination may be improved. In a flex fuelvehicle, by determining fuel ethanol content after each refueling event,a resultant ethanol content in the fuel caused by mixing of fuelpreviously present in the tank and the newly delivered fuel may beestimated and used for determining air-fuel ratio. The technical effectof periodically estimating fuel aging in gasoline is that degraded fuelmay be timely identified and reported to the operator to maintain enginefunctionality. Overall, by adjusting engine operation based on anestimated fuel ethanol content or fuel age, engine performance, fuelefficiency, and emissions quality may be improved.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an example embodiment of a cylinder of aninternal combustion engine coupled to a hybrid vehicle.

FIG. 2 schematically depicts an example embodiment of a fuel system,configured for port injection and direct injection that may be used withthe engine of FIG. 1.

FIG. 3 shows a flow chart illustrating a first method for determiningethanol content in a flex-fuel powered vehicle.

FIG. 4 shows a flow chart illustrating a first method for determiningaging in gasoline.

FIG. 5 shows a flow chart illustrating a second method for determiningethanol content in fuel.

FIG. 6 shows a flow chart illustrating a second method for determiningaging in gasoline.

FIG. 7 shows a plot illustrating change in fuel rail pressure inresponse to a fuel pump stroke.

FIG. 8 shows a plot illustrating change in fuel rail pressure inresponse to a fuel injection.

FIG. 9 shows a plot illustrating resonant pulsations in fuel railpressure in response to a fuel injection.

FIG. 10 shows a plot illustrating damping of pressure pulsations in fuelrail after a fuel injection.

FIG. 11 shows a relationship between ethanol content in fuel and thedamping of fuel rail pressure pulsations.

FIG. 12 shows a relationship between ethanol content in fuel and dampingcoefficient.

FIG. 13 shows a relation between ethanol content in fuel and the speedof sound through fuel.

FIG. 14 shows an example determination of fuel ethanol content usingfuel rail pressure.

FIG. 15 shows an example determination of fuel age using fuel railpressure.

FIG. 16 shows a flow chart illustrating a third method for determiningethanol content in fuel.

FIG. 17 shows a flow chart illustrating a third method for determiningaging in fuel.

FIG. 18 shows an example determination of fuel ethanol content using anultrasonic signal.

FIG. 19 shows an example determination of fuel age using an ultrasonicsignal.

DETAILED DESCRIPTION

The following description relates to systems and methods for estimatingethanol content, water content, and an age of fuel contained in anengine fuel tank. An example embodiment of a cylinder in an internalcombustion engine with each of a direct fuel injector and a port fuelinjector is given in FIG. 1. FIG. 2 depicts a fuel system that may beused with the engine of FIG. 1. An engine controller may be configuredto perform example routines, such as according to the methods describedin FIGS. 3-6 for determining ethanol and water content in fuel and fuelaging based on fuel rail temperature, change in fuel rail pressure, fuelrail pressure pulsation frequency, and a damping co-efficient ofpressure pulsations following fuel injection or a fuel pump stroke. Theengine controller may also be configured to determine fuel ethanolcontent and fuel age based on attenuation of ultrasonic signal in fuel,as described in FIGS. 17-18. Example plots 7-10 show variation inpressure due to fuel pump stroke, fuel injection, resonance frequencyvibrations, and damping of pressure vibrations, respectively. An examplerelationship between fuel ethanol content and fuel rail pressurepulsations, damping coefficient of pressure pulsations, and speed ofsound in fuel, respectively are shown in FIGS. 11-13. Exampledeterminations of the fuel ethanol content and fuel age are shown inFIGS. 14, 15, 18 and 19.

FIG. 1 depicts an example of a cylinder 14 of an internal combustionengine 10, which may be included in an engine system 100 in a vehicle 5.Engine 10 may be controlled at least partially by a control systemincluding controller 12 and by input from a vehicle operator 130 via aninput device 132. In this example, input device 132 includes anaccelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal PP. Cylinder (herein also “combustionchamber”) 14 of engine 10 may include combustion chamber walls 136 withpiston 138 positioned therein. Piston 138 may be coupled to crankshaft140 so that reciprocating motion of the piston is translated intorotational motion of the crankshaft. Crankshaft 140 may be coupled to atleast one drive wheel of the passenger vehicle via a transmissionsystem. Further, a starter motor (not shown) may be coupled tocrankshaft 140 via a flywheel to enable a starting operation of engine10.

Cylinder 14 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 14. In some examples, oneor more of the intake passages may include a boosting device such as aturbocharger or a supercharger. For example, FIG. 1 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 162 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 162 may be positioned downstreamof compressor 174 as shown in FIG. 1, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 14. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 178.Sensor 128 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 178 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 14. In some examples, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 via actuator 152.Similarly, exhaust valve 156 may be controlled by controller 12 viaactuator 154. During some conditions, controller 12 may vary the signalsprovided to actuators 152 and 154 to control the opening and closing ofthe respective intake and exhaust valves. The position of intake valve150 and exhaust valve 156 may be determined by respective valve positionsensors (not shown). The valve actuators may be of the electric valveactuation type or cam actuation type, or a combination thereof. Theintake and exhaust valve timing may be controlled concurrently or any ofa possibility of variable intake cam timing, variable exhaust camtiming, dual independent variable cam timing or fixed cam timing may beused. Each cam actuation system may include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.For example, cylinder 14 may alternatively include an intake valvecontrolled via electric valve actuation and an exhaust valve controlledvia cam actuation including CPS and/or VCT. In other examples, theintake and exhaust valves may be controlled by a common valve actuatoror actuation system, or a variable valve timing actuator or actuationsystem.

Cylinder 14 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. In one example, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some examples, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 14 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some examples, each cylinder of engine 10 may be configured with oneor more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 14 is shown including two fuel injectors 166 and 170.Fuel injectors 166 and 170 may be configured to deliver fuel receivedfrom fuel system 8. As elaborated with reference to FIG. 2, the fuelsystem 8 may include one or more fuel tanks, fuel pumps, fuel rails, andfuel rail sensors. Fuel injector 166 is shown coupled directly tocylinder 14 for injecting fuel directly therein in proportion to thepulse width of signal FPW-1 received from controller 12 via electronicdriver 168. In this manner, fuel injector 166 provides what is known asdirect injection (hereafter referred to as “DI”) of fuel into combustioncylinder 14. While FIG. 1 shows injector 166 positioned to one side ofcylinder 14, it may alternatively be located overhead of the piston,such as near the position of spark plug 192. Such a position may improvemixing and combustion when operating the engine with an alcohol-basedfuel due to the lower volatility of some alcohol-based fuels.Alternatively, the injector may be located overhead and near the intakevalve to improve mixing. Fuel may be delivered to fuel injector 166 froma fuel tank of fuel system 8 via a high pressure fuel pump, and a fuelrail. Further, the fuel rail may have a pressure sensor and atemperature sensor providing a signal to controller 12.

Fuel injector 170 is shown arranged in intake passage 146, rather thanin cylinder 14, in a configuration that provides what is known as portinjection of fuel (hereafter referred to as “PFI”) into the intake portupstream of cylinder 14. Fuel injector 170 may inject fuel, receivedfrom fuel system 8, in proportion to the pulse width of signal FPW-2received from controller 12 via electronic driver 171. Note that asingle driver 168 or 171 may be used for both fuel injection systems, ormultiple drivers, for example driver 168 for fuel injector 166 anddriver 171 for fuel injector 170, may be used, as depicted.

In an alternate example, each of fuel injectors 166 and 170 may beconfigured as direct fuel injectors for injecting fuel directly intocylinder 14. In still another example, each of fuel injectors 166 and170 may be configured as port fuel injectors for injecting fuel upstreamof intake valve 150. In yet other examples, cylinder 14 may include onlya single fuel injector that is configured to receive different fuelsfrom the fuel systems in varying relative amounts as a fuel mixture, andis further configured to inject this fuel mixture either directly intothe cylinder as a direct fuel injector or upstream of the intake valvesas a port fuel injector. As such, it should be appreciated that the fuelsystems described herein should not be limited by the particular fuelinjector configurations described herein by way of example.

Fuel may be delivered by both injectors to the cylinder during a singlecycle of the cylinder. For example, each injector may deliver a portionof a total fuel injection that is combusted in cylinder 14. Further, thedistribution and/or relative amount of fuel delivered from each injectormay vary with operating conditions, such as engine load, knock, andexhaust temperature, such as described herein below. The port injectedfuel may be delivered during an open intake valve event, closed intakevalve event (e.g., substantially before the intake stroke), as well asduring both open and closed intake valve operation. Similarly, directlyinjected fuel may be delivered during an intake stroke, as well aspartly during a previous exhaust stroke, during the intake stroke, andpartly during the compression stroke, for example. As such, even for asingle combustion event, injected fuel may be injected at differenttimings from the port and direct injector. Furthermore, for a singlecombustion event, multiple injections of the delivered fuel may beperformed per cycle. The multiple injections may be performed during thecompression stroke, intake stroke, or any appropriate combinationthereof.

Fuel injectors 166 and 170 may have different characteristics. Theseinclude differences in size, for example, one injector may have a largerinjection hole than the other. Other differences include, but are notlimited to, different spray angles, different operating temperatures,different targeting, different injection timing, different spraycharacteristics, different locations etc. Moreover, depending on thedistribution ratio of injected fuel among injectors 170 and 166,different effects may be achieved.

Fuel tanks in fuel system 8 may hold fuels of different fuel types, suchas fuels with different fuel qualities and different fuel compositions.The differences may include different alcohol content, different watercontent, different concentrations of lighter and heavier hydrocarbonends, different octane, different heats of vaporization, different fuelblends, and/or combinations thereof etc. One example of fuels withdifferent heats of vaporization could include gasoline as a first fueltype with a lower heat of vaporization and ethanol as a second fuel typewith a greater heat of vaporization. In another example, the engine mayuse a flexible fuel containing alcohol such as E85 (which isapproximately 85% ethanol and 15% gasoline) or M85 (which isapproximately 85% methanol and 15% gasoline) as a second fuel type.Other feasible substances include water, methanol, a mixture of alcoholand water, a mixture of water and ethanol, a mixture of alcohols, etc.

In still another example, both fuels may be alcohol blends with varyingalcohol composition wherein the first fuel type may be a gasolinealcohol blend with a lower concentration of alcohol, such as Eli) (whichis approximately 10% ethanol), while the second fuel type may be agasoline alcohol blend with a greater concentration of alcohol, such asE85 (which is approximately 85% ethanol). Additionally, the first andsecond fuels may also differ in other fuel qualities such as adifference in temperature, viscosity, octane number, etc. Moreover, fuelcharacteristics of one or both fuel tanks may vary frequently, forexample, due to day to day variations in tank refilling.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown asnon-transitory read only memory chip 110 in this particular example forstoring executable instructions, random access memory 112, keep alivememory 114, and a data bus. Controller 12 may receive various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; absolute manifold pressure signal (MAP) from sensor124; fuel rail pressure from a fuel rail pressure sensor; fuel railtemperature from a fuel rail temperature sensor; and ultrasonic signalamplitude from an ultrasonic signal sensor. Engine speed signal, RPM,may be generated by controller 12 from signal PIP. Manifold pressuresignal MAP from a manifold pressure sensor may be used to provide anindication of vacuum, or pressure, in the intake manifold. Thecontroller 12 receives signals from the various sensors of FIG. 1 andemploys the various actuators of FIG. 1 to adjust engine operation basedon the received signals and instructions stored on a memory of thecontroller.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine. As such, each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc. It will beappreciated that engine 10 may include any suitable number of cylinders,including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Further, each ofthese cylinders can include some or all of the various componentsdescribed and depicted by FIG. 1 with reference to cylinder 14.

In some examples, vehicle 5 may be a hybrid vehicle with multiplesources of torque available to one or more vehicle wheels 55. In otherexamples, vehicle 5 is a conventional vehicle with only an engine, or anelectric vehicle with only electric machine(s). In the example shown,vehicle 5 includes engine 10 and an electric machine 52. Electricmachine 52 may be a motor or a motor/generator. Crankshaft 140 of engine10 and electric machine 52 are connected via a transmission 54 tovehicle wheels 55 when one or more clutches 56 are engaged. In thedepicted example, a first clutch 56 is provided between crankshaft 140and electric machine 52, and a second clutch 56 is provided betweenelectric machine 52 and transmission 54. Controller 12 may send a signalto an actuator of each clutch 56 to engage or disengage the clutch, soas to connect or disconnect crankshaft 140 from electric machine 52 andthe components connected thereto, and/or connect or disconnect electricmachine 52 from transmission 54 and the components connected thereto.Transmission 54 may be a gearbox, a planetary gear system, or anothertype of transmission. The powertrain may be configured in variousmanners including as a parallel, a series, or a series-parallel hybridvehicle.

Electric machine 52 receives electrical power from a traction battery 58to provide torque to vehicle wheels 55. Electric machine 52 may also beoperated as a generator to provide electrical power to charge battery58, for example during a braking operation.

FIG. 2 schematically depicts an example embodiment 200 of a fuel system,such as fuel system 8 of FIG. 1. Fuel system 200 may be operated todeliver fuel to an engine, such as engine 10 of FIG. 1.

Fuel system 200 includes a fuel storage tank 210 for storing the fuelon-board the vehicle, a lower pressure fuel pump (LPP) 212, and a higherpressure fuel pump (HPP) 214 (herein also referred to as fuel pump 214).Fuel may be provided to fuel tank 210 via fuel filling passage 204. Inone example, LPP 212 may be an electrically-powered lower pressure fuelpump disposed at least partially within fuel tank 210. LPP 212 may beoperated by a controller 222 (e.g., controller 12 of FIG. 1) to providefuel to HPP 214 via fuel passage 218. LPP 212 can be configured as whatmay be referred to as a fuel lift pump. As one example, LPP 212 may be aturbine (e.g., centrifugal) pump including an electric (e.g., DC) pumpmotor, whereby the pressure increase across the pump and/or thevolumetric flow rate through the pump may be controlled by varying theelectrical power provided to the pump motor, thereby increasing ordecreasing the motor speed. For example, as the controller reduces theelectrical power that is provided to lift pump 212, the volumetric flowrate and/or pressure increase across the lift pump may be reduced. Thevolumetric flow rate and/or pressure increase across the pump may beincreased by increasing the electrical power that is provided to liftpump 212. As one example, the electrical power supplied to the lowerpressure pump motor can be obtained from an alternator or other energystorage device on-board the vehicle (not shown), whereby the controlsystem can control the electrical load that is used to power the lowerpressure pump. Thus, by varying the voltage and/or current provided tothe lower pressure fuel pump, the flow rate and pressure of the fuelprovided at the inlet of the higher pressure fuel pump 214 is adjusted.

LPP 212 may be fluidly coupled to a filter 217, which may remove smallimpurities contained in the fuel that could potentially damage fuelhandling components. A check valve 213, which may facilitate fueldelivery and maintain fuel line pressure, may be positioned fluidlyupstream of filter 217. With check valve 213 upstream of the filter 217,the compliance of low-pressure passage 218 may be increased since thefilter may be physically large in volume. Furthermore, a pressure reliefvalve 219 may be employed to limit the fuel pressure in low-pressurepassage 218 (e.g., the output from lift pump 212). Relief valve 219 mayinclude a ball and spring mechanism that seats and seals at a specifiedpressure differential, for example. The pressure differential set-pointat which relief valve 219 may be configured to open may assume varioussuitable values; as a non-limiting example the set-point may be 6.4 baror 5 bar (g). An orifice 223 may be utilized to allow for air and/orfuel vapor to bleed out of the lift pump 212. This bleed at orifice 223may also be used to power a jet pump used to transfer fuel from onelocation to another within the tank 210. In one example, an orificecheck valve (not shown) may be placed in series with orifice 223. Insome embodiments, fuel system 8 may include one or more (e.g., a series)of check valves fluidly coupled to low-pressure fuel pump 212 to impedefuel from leaking back upstream of the valves. In this context, upstreamflow refers to fuel flow traveling from fuel rails 250, 260 towards LPP212 while downstream flow refers to the nominal fuel flow direction fromthe LPP towards the HPP 214 and thereon to the fuel rails.

Fuel lifted by LPP 212 may be supplied at a lower pressure into a fuelpassage 218 leading to an inlet 203 of HPP 214. HPP 214 may then deliverfuel into a first fuel rail 250 coupled to one or more fuel injectors ofa first group of direct injectors 252 (herein also referred to as afirst injector group). Fuel lifted by the LPP 212 may also be suppliedto a second fuel rail 260 coupled to one or more fuel injectors of asecond group of port injectors 262 (herein also referred to as a secondinjector group). HPP 214 may be operated to raise the pressure of fueldelivered to the first fuel rail above the lift pump pressure, with thefirst fuel rail coupled to the direct injector group operating with ahigh pressure. As a result, high pressure DI may be enabled while PFImay be operated at a lower pressure.

While each of first fuel rail 250 and second fuel rail 260 are showndispensing fuel to four fuel injectors of the respective injector group252, 262, it will be appreciated that each fuel rail 250, 260 maydispense fuel to any suitable number of fuel injectors. As one example,first fuel rail 250 may dispense fuel to one fuel injector of firstinjector group 252 for each cylinder of the engine while second fuelrail 260 may dispense fuel to one fuel injector of second injector group262 for each cylinder of the engine. Controller 222 can individuallyactuate each of the port injectors 262 via a port injection driver 237and actuate each of the direct injectors 252 via a direct injectiondriver 238. The controller 222, the drivers 237, 238 and other suitableengine system controllers can comprise a control system. While thedrivers 237, 238 are shown external to the controller 222, it should beappreciated that in other examples, the controller 222 can include thedrivers 237, 238 or can be configured to provide the functionality ofthe drivers 237, 238. Controller 222 may include additional componentsnot shown, such as those included in controller 12 of FIG. 1.

HPP 214 may be an engine-driven, positive-displacement pump. As onenon-limiting example, HPP 214 may be a BOSCH HDP5 HIGH PRESSURE PUMP,which utilizes a solenoid activated control valve (e.g., fuel volumeregulator, magnetic solenoid valve, etc.) to vary the effective pumpvolume of each pump stroke. The outlet check valve of HPP ismechanically controlled and not electronically controlled by an externalcontroller. HPP 214 may be mechanically driven by the engine in contrastto the motor driven LPP 212. HPP 214 includes a pump piston 228, a pumpcompression chamber 205 (herein also referred to as compressionchamber), and a step-room 227. Pump piston 228 receives a mechanicalinput from the engine crank shaft or cam shaft via cam 230, therebyoperating the HPP according to the principle of a cam-drivensingle-cylinder pump. A sensor (not shown in FIG. 2) may be positionednear cam 230 to enable determination of the angular position of the cam(e.g., between 0 and 360 degrees), which may be relayed to controller222.

A lift pump fuel pressure sensor 231 may be positioned along fuelpassage 218 between lift pump 212 and higher pressure fuel pump 214. Inthis configuration, readings from sensor 231 may be interpreted asindications of the fuel pressure of lift pump 212 (e.g., the outlet fuelpressure of the lift pump) and/or of the inlet pressure of higherpressure fuel pump. Readings from sensor 231 may be used to assess theoperation of various components in fuel system 200, to determine whethersufficient fuel pressure is provided to higher pressure fuel pump 214 sothat the higher pressure fuel pump ingests liquid fuel and not fuelvapor, and/or to minimize the average electrical power supplied to liftpump 212.

First fuel rail 250 includes a first fuel rail pressure sensor 248 and afirst fuel rail temperature sensor 232 for providing an indication ofdirect injection fuel rail pressure and first fuel rail temperature,respectively, to the controller 222. Likewise, second fuel rail 260includes a second fuel rail pressure sensor 258 and a first fuel railtemperature sensor 232 for providing an indication of port injectionfuel rail pressure and second fuel rail temperature, respectively, tothe controller 222.

The fuel rail pressure sensors 248 and/or 258 and the fuel railtemperature sensors 232 and/or 234 may be used to determine ethanolcontent and/or age of fuel in the fuel tank 210. For flexible fuels(containing ethanol), the fuel ethanol content is a percentage ofethanol in fuel contained in a fuel tank 210 of an engine fuel systemFor gasoline, fuel age is an indication of change in fuel constituentsover time due to vaporization of the fuel's lighter, more volatile ends.The vaporized part of the fuel may be routed either to a fuel vaporstorage canister or into the atmosphere. The fuel aging process is afunction of duration and conditions (such as temperature variationduring diurnal cycles) at which the fuel is stored in the fuel tank. Inone example, if the fuel is stored at a higher temperature (such asduring hot ambient conditions) for a longer duration, the vaporizationprocess may be expedited, thereby increasing the fuel age. In a hybridvehicle, the fuel age may be estimated periodically after completion ofa threshold distance of travel and/or duration of travel since animmediately previous fuel age estimation. In a flex-fuel vehicle, thefuel ethanol content may be estimated periodically at least within afirst threshold distance of travel and/or duration of travel after arefueling event and the fuel water content may be estimated periodicallyafter completion of a second threshold distance of travel and/orduration of travel since an immediately previous fuel age estimation,the second threshold distance of travel and/or duration of travel beinghigher than the first threshold distance of travel and/or duration oftravel.

A volume fraction of ethanol in fuel, a volume fraction of water infuel, and an age of fuel contained in a fuel tank 210 may be estimatedbased on an estimated fuel rail temperature and one of a pulsationfrequency, a change in pressure, and a damping coefficient of pressurepulsations as estimated after a fuel injection or a pump stroke. Thechange in pressure during a fuel pump stroke or fuel injection may be afunction of the fuel bulk modulus, the damping coefficient of pressurepulsations in a fuel rail (such as first fuel rail 250) immediatelyafter a fuel pump stroke or fuel injection may be a function of the fuelviscosity, and the resonant frequency of the pressure pulsations in thefuel rail may be a function of the speed of sound in fuel. In responseto the estimation of the fuel ethanol content, water content, and fuelage, one or more engine operating parameters may be adjusted. As anexample, the amount of injected fuel during a cold start may beincreased in response to an increase in ethanol volume fraction or anincrease in fuel age, and the commanded air-fuel ratio may be decreasedin response to an increase in ethanol volume fraction, and spark timingmay be advanced in response to an increase in ethanol volume fraction.Methods for fuel ethanol content, water content, and/or agingdetermination is discussed in details with reference to FIGS. 3-6.

In an alternate embodiment, fuel rail temperature sensors 232 and 234may be eliminated and fuel rail temperature may be determined based onfuel rail pressure variations. If fuel rail temperature is not known,such as in a port injection system without a fuel rail temperaturesensor, the volume fractions of ethanol and water in fuel and the fuelrail temperature may be estimated in a flex fuel vehicle based on atleast three of a pulsation frequency, a change in pressure, and adamping coefficient of pressure pulsations as estimated after a fuelinjection or a pump stroke. In a hybrid vehicle, the fuel age and thefuel rail temperature may be estimated based on at least two of thepulsation frequency, a change in pressure, and a damping coefficient ofpressure pulsations as estimated after a fuel injection or a pumpstroke. Methods for fuel rail temperature determination is discussed indetails with reference to FIGS. 5-6.

An engine speed sensor 233 can be used to provide an indication ofengine speed to the controller 222. The indication of engine speed canbe used to identify the speed of higher pressure fuel pump 214, sincethe pump 214 is mechanically driven by the engine 202, for example, viathe crankshaft or camshaft.

First fuel rail 250 is coupled to an outlet 208 of HPP 214 along fuelpassage 278. A check valve 274 and a pressure relief valve (also knownas pump relief valve) 272 may be positioned between the outlet 208 ofthe HPP 214 and the first (DI) fuel rail 250. The pump relief valve 272may be coupled to a bypass passage 279 of the fuel passage 278. Outletcheck valve 274 opens to allow fuel to flow from the high pressure pumpoutlet 208 into a fuel rail only when a pressure at the outlet of directinjection fuel pump 214 (e.g., a compression chamber outlet pressure) ishigher than the fuel rail pressure. The pump relief valve 272 may limitthe pressure in fuel passage 278, downstream of HPP 214 and upstream offirst fuel rail 250. For example, pump relief valve 272 may limit thepressure in fuel passage 278 to 200 bar. Pump relief valve 272 allowsfuel flow out of the DI fuel rail 250 toward pump outlet 208 when thefuel rail pressure is greater than a predetermined pressure. Valves 244and 242 work in conjunction to keep the low pressure fuel rail 260pressurized to a pre-determined low pressure. Pressure relief valve 242helps limit the pressure that can build in fuel rail 260 due to thermalexpansion of fuel.

Based on engine operating conditions, fuel may be delivered by one ormore port injectors 262 and direct injectors 252. For example, duringhigh load conditions, fuel may be delivered to a cylinder on a givenengine cycle via only direct injection, wherein port injectors 262 aredisabled. In another example, during mid load conditions, fuel may bedelivered to a cylinder on a given engine cycle via each of direct andport injection. As still another example, during low load conditions,engine starts, as well as warm idling conditions, fuel may be deliveredto a cylinder on a given engine cycle via only port injection, whereindirect injectors 252 are disabled.

It is noted here that the high pressure pump 214 of FIG. 2 is presentedas an illustrative example of one possible configuration for a highpressure pump. Components shown in FIG. 2 may be removed and/or changedwhile additional components not presently shown may be added to pump 214while still maintaining the ability to deliver high-pressure fuel to adirect injection fuel rail and a port injection fuel rail.

In an alternate embodiment, the fuel system may include only the portinjectors 262 instead of both direct injectors and port injectors 262.Also, in case of fuel injection via port injectors 262, the second fuelrail 260 may be eliminated. A fuel temperature sensor 243 may be housedin the fuel tank to facilitate estimation of fuel temperature in thetank. An ultrasonic signal generator 240 may be coupled to a wall of thefuel tank 210, and an ultrasonic sensor 241 may be coupled to thegenerator 240. The ultrasonic signal generator 240 may generateultrasonic waves which may pass through the fuel in the tank. The wavesmay get reflected from a fixed object such as a wall of the tankopposite to the wall on which the signal generator 240 is mounted. Inthis way, the ultrasonic signal may be generated by an ultrasonic signalgenerator coupled to a first wall of a fuel tank, and the ultrasonicsignal may be detected by an ultrasonic sensor coupled to the firstwall, adjacent to the ultrasonic signal generator, each of theultrasonic signal generator and the ultrasonic sensor being immersed infuel. A speed of sound in fuel may be estimated based on a time oftravel of a reflected ultrasonic signal to and from a second wall,opposite to the first wall, and a distance between the first wall andthe second wall. Also, an attenuation co-efficient of ultrasonic signalin fuel may be estimated based on a difference in amplitude between thegenerated ultrasonic signal and the reflected ultrasonic signal. Avolume fraction of ethanol in fuel or an age of the fuel contained inthe fuel tank may be estimated based on each of the fuel temperature,the speed of sound in the fuel, and the attenuation co-efficient ofultrasonic signal in the fuel. Methods for fuel ethanol content and/oraging determination using an ultrasonic signal are discussed in detailswith reference to FIGS. 15-16.

Controller 222 can also control the operation of each of fuel pumps 212,and 214 to adjust an amount, pressure, flow rate, etc., of a fueldelivered to the engine. As one example, controller 222 can vary apressure setting, a pump stroke amount, a pump duty cycle command and/orfuel flow rate of the fuel pumps to deliver fuel to different locationsof the fuel system. A driver (not shown) electronically coupled tocontroller 222 may be used to send a control signal to the low pressurepump, as required, to adjust the output (e.g., speed, flow output,and/or pressure) of the low pressure pump.

In this way, the systems discussed above at FIGS. 1 and 2 may enable anengine system comprising: a controller with computer readableinstructions stored on non-transitory memory that, when executed, causethe controller to: upon completion of a refueling event, estimate a fuelethanol and water content based on each of a temperature of a fuel railand two fuel rail pressure factors, and adjust one or more of amount ofinjected fuel and spark timing, based on the estimated fuel ethanol andwater content, or upon completion of a threshold duration since animmediately prior fuel age estimation, estimate fuel age based on eachof the temperature of the fuel rail and the fuel rail pressure factor,and adjust one or more of amount of injected fuel and fuel injectiontiming. The fuel rail pressure factor may include one or more of achange in fuel rail pressure responsive to a stroke of a fuel pump orfuel injection, a damping coefficient of pressure pulsations in a fuelrail immediately after the stroke or injection, and a resonant frequencyof the pressure pulsations in the fuel rail immediately after the strokeor injection.

FIG. 3 shows an example method 300 that can be implemented to estimate avolume fraction of ethanol and water in fuel. Instructions for carryingout method 300 and the rest of the methods included herein may beexecuted by a controller based on instructions stored on a memory of thecontroller and in conjunction with signals received from sensors of theengine system, such as the sensors described above with reference toFIGS. 1 and 2. The controller may employ engine actuators of the enginesystem to adjust engine operation, according to the methods describedbelow.

At 302, current vehicle and engine operating parameters may bedetermined. The parameters may include vehicle speed, torque demand,engine speed, engine temperature, etc. The controller may estimate anamount of fuel supplied to the fuel injectors (direct injectors and/orport injectors) via the first fuel rail (such as first fuel rail 250 inFIG. 2) coupled to the direct injectors (such as direct injectors 252 inFIG. 2) and the second fuel rail (such as second fuel rail 260 in FIG.2) coupled to the port injectors (such as port injectors 262 in FIG. 2).The controller may monitor operation of a fuel pump (such as highpressure pump 214 in FIG. 2) such as timing of a fuel pump stroke.

At 304, the routine includes determining if conditions are met for fuelethanol content determination. Ethanol content determination may becarried out in an engine using a flexible fuel containing ethanol (suchas E85 containing 85% ethanol). Thus, in some examples, the ethanolcontent determination may be carried out only in vehicles configured tooperate with ethanol fuel (e.g., flex fuel vehicles). In one example,ethanol content estimation may be carried out after a vehicle refuelingis detected.

The conditions may include the vehicle being propelled via engine torquewith fuel being supplied to the injectors via a fuel rail (such as thefirst fuel rail). The conditions may further include a refueling eventhaving occurred within a threshold amount of time. During refueling witha fuel that may contain ethanol, fuel remaining in the fuel tank may mixwith the fuel that is being dispensed, resulting in a fuel blend ofexisting and new fuel. The ethanol content and the water content of thefuel blend may be different from the ethanol content and water contentof the existing fuel or the delivered fuel, and the ethanol content ofthe fuel blend may be estimated within a threshold duration (or athreshold distance of travel) after the refueling event. For example,such estimations may be carried out within 1 day of refueling or within10 miles of travel after refueling. Due to the amount of water absorbedby ethanol may change over time (between refueling events), theconditions may further include a threshold duration of time elapsingsince a prior fuel ethanol content estimation. For example, suchestimations may be carried out periodically, such as every 15 days. Ifit is determined that conditions are not met for fuel ethanol contentdetermination, at 306, current engine operation may be continued withoutfuel ethanol content determination. Engine operation may includesupplying fuel to one or more fuel injectors via one or more fuel rails.

If it is determined that conditions are met for fuel ethanol contentdetermination, at 308, fuel rail temperature may be estimated via a fuelrail temperature sensor (such as first fuel rail temperature sensor 232in FIG. 2) coupled to the fuel rail. Alternatively, fuel railtemperature may be estimated using a physics-based or empirical modelrelating fuel rail temperature to the engine operating conditions andstates.

At 310, two or more of a resonant frequency (f) of pressure pulsations,a change in fuel rail pressure (δp), and a damping coefficient (α) ofpressure pulsations in the fuel rail may be estimated after a fuelinjection or a pump stroke. In one example, fuel bulk modulus may beestimated based on a function of the change in fuel rail pressure (δp)caused by a pump stroke or injection event, a speed of sound in fuel maybe estimated based on a function of the resonant frequency (f) ofpressure pulsations in the fuel rail due to a fuel pump stroke or a fuelinjection and a fuel viscosity may be estimated based on a function ofthe damping coefficient (α) of pressure pulsations in the fuel railafter a fuel pump stroke or a fuel injection.

In order to estimate one or more of the change in fuel rail pressure(δp), resonant frequency (f) of pressure pulsations, and a dampingcoefficient (α) of pressure pulsations, a pump stroke of a high pressurefuel pump (such as HP fuel pump 214 in FIG. 2) housed in a fuel tank maybe determined. The pump stroke may correspond to operation of the pumpto deliver fuel from the fuel tank to the direct injector fuel rail viaa fuel line. A change (increase) in fuel rail pressure may be determinedvia fuel rail pressure sensors (such as pressure sensor 248 in FIG. 2)immediately after the pump stroke. As the pump is operated to transferfuel from the fuel tank to the fuel rail, the fuel rail pressure mayincrease during a pump stroke. As an example, during the pump stroke,the controller may estimate a change in a magnitude of pressure or aslope of pressure.

The controller may determine a fuel direct injection event that resultsin at least a threshold change (decrease) in the amount of fuelremaining in the rail. Fuel may be injected via one or more directinjectors (such as direct injectors 252) coupled to a fuel rail. Aduration of fuel injection may be estimated. The duration may include atime elapsed between a start of fuel injection to a completion of fuelinjection to a certain cylinder at a single fuel injection event. Fuelmay be pumped from the fuel tank to the direct injectors via the fuelline and rail. The decrease in the amount of fuel remaining in the railfollowing the injection event may result in a decrease in the fuel railpressure. A change (decrease) in fuel rail pressure may be determinedvia fuel rail pressure sensors (such as pressure sensor 248 in FIG. 2)immediately after the fuel injection. In this way, a change in fuel railpressure may be estimated immediately after a fuel injection or a fuelpump stroke.

After the pump stroke or fuel injection, pressure pulsations may begenerated at the fuel rail. The fuel rail pulsations may have a resonantfrequency. The resonant frequency of pressure pulsations in the fuelrail may be determined via processing the pressure signal from fuel railpressure sensors (such as pressure sensor 248 in FIG. 2) after the pumpstroke or fuel injection.

The pressure pulsations generated at the fuel rail after the fuelinjection or the pump stroke may be damped with the amplitude of thepulsations decreasing over time. The amplitude of the pressurepulsations may decay at an exponential rate. A damping coefficient ofthe pressure pulsations in the fuel rail may be determined. Anexponential curve may be fit to the decaying amplitude profile of thepressure pulsations and/or an exponential function may be fit to thepressure signal envelope. In one example, the damping coefficient may bea constant in the exponential function. In another example, anexponentially damped sinusoid curve may be fitted to the decayingpressure pulsations. The damping coefficient may be a constant in theexponential function (multiplied by the sinusoid). In yet anotherexample, the damping coefficient may be estimated using Prony analysis.The Fast Fourier Transform (FFT) of the pressure signal may also be usedfor estimating the damping coefficient α s amplitude of the resonantfrequency component obtained from FFT is a function of the dampingcoefficient.

FIG. 7 shows an example plot 700 illustrating a change in fuel railpressure over time. The y-axis denotes fuel rail pressure (in psi) andthe x-axis denotes time in (sec). The pressure may be estimated via apressure sensor coupled to the fuel rail (such as pressure sensor 248 inFIG. 2). At time t1, a fuel pump stroke may begin and continue untiltime t2. Between time t1 and t2, as shown by line 702, there is a steadyincrease in fuel tank pressure. After the completion of the pump stroke,the pressure may plateau. The difference in pressure (API) between thepressure at time t1 and the pressure at time t2 may be the change infuel rail pressure immediately following a fuel pump stroke. Also, theslope of the fuel rail pressure plot between time t1 and t2 may beestimated.

FIG. 8 shows an example plot 800 illustrating a change in fuel railpressure over time. The y-axis denotes fuel rail pressure (in psi) andthe x-axis denotes time in (sec). The pressure may be estimated via apressure sensor coupled to the fuel rail (such as pressure sensor 248 inFIG. 2). The plot is generated based on an experiment where the fuelinjection duration is set at 2 ms. A first fuel injection may take placeat time t1 followed by a second fuel injection at time t2. As seen inline 802, ΔP2 may be the difference in fuel rail pressure immediatelybefore and after the first fuel injection and ΔP3 may be the differencein fuel rail pressure immediately before and after the second fuelinjection.

FIG. 9 shows an example plot 900 illustrating resonant frequencypulsations in the fuel rail after a pump stroke. The y-axis denotes fuelrail pressure (in psi) and the x-axis denotes time in (sec). Thepressure may be estimated via a pressure sensor coupled to the fuel rail(such as pressure sensor 248 in FIG. 2). As seen in line 902, pressurepulsations troughs occur at time t1, t2, t3, etc. The frequency may bedetermined using Fast Fourier Transform (FFT) or Prony analysis.

FIG. 10 shows an example plot 1000 illustrating damping of pressurepulsations in the fuel rail after a fuel injection. The y-axis denotedfuel rail pressure (in psi) and the x-axis denotes time (in sec). Thepressure may be estimated via a pressure sensor coupled to the fuel rail(such as pressure sensor 248 in FIG. 2). As seen in line 1002, anexponential curve may be fit to the decaying amplitudes of the pressurepulsations. The damping coefficient may be estimated based on theexponential function of the fitted curve. The damping coefficient mayalso be estimated based on the exponential function of a damped sinusoidcurve, or using Prony analysis, or FFT.

At 312, fuel ethanol content (volume fraction) may be estimated based onthe fuel rail temperature, the resonant frequency (f) of pressurepulsations, the change in fuel rail pressure (δp), and the dampingcoefficient (α) of pressure pulsations in the fuel rail as estimatedafter a fuel injection or a pump stroke. During conditions when fuelwater content is not known, the fuel ethanol content may be estimated asa function of fuel rail temperature and two of the resonant frequency(f) of pressure pulsations, the change in fuel rail pressure (δp), andthe damping coefficient (α) of pressure pulsations in the fuel rail.Said another way, the fuel ethanol content may be estimated based on thefuel rail temperature and at least two of the estimated fuel bulkmodulus, the speed of sound in fuel, and the fuel viscosity. In oneexample, a first estimate of ethanol content may be computed as afunction of the fuel rail temperature, f, and a, and a second estimatemay be computed as a function of the fuel rail temperature, δp, and a.Ethanol content may then be estimated as a weighted average of the firstand second estimates. A weighted average of the estimates from based ondifferent functions may be used to improve accuracy.

During conditions when fuel water content is known fuel ethanol contentmay be estimated as one of a first function of resonant frequency (f)and fuel rail temperature, a second function of change in fuel railpressure (δp)in fuel and fuel rail temperature, and as a third functionof damping coefficient (α) and fuel rail temperature.

FIG. 11 shows an example plot 1100 depicting a relationship betweenethanol content in fuel and a normalized root mean square (RMS) envelopeof fuel rail pressure pulsations. The x-axis denotes time and the y-axisdenotes a RMS envelope of rail pressure pulsations in fuel containing 0%ethanol, 50% ethanol, or 100% ethanol. As seen from the plot, sinceethanol has higher viscosity relative to gasoline, the decay rate of thepressure pulsations becomes faster with an increase in fuel ethanolcontent.

FIG. 12 shows an example plot 1200 depicting a relationship betweenethanol content in fuel and a damping coefficient (α) of fuel railpressure pulsations. The x-axis denotes a measurement number and they-axis denotes a damping coefficient (in Hz) in fuel containing 0%ethanol, 50% ethanol, or 100% ethanol. As seen from the plot, thedamping coefficient increases with an increase in fuel ethanol content.

FIG. 13 shows an example plot 1300 depicting a relation between ethanolcontent in fuel and the speed of sound through fuel. The speed of soundmay be estimated based on the resonant frequency (f) of pressurepulsations in fuel. The x-axis denotes ethanol volume fraction (%) infuel and the y-axis shows a speed of sound (in m/s) in fuel. The speedof sound may change non-monotonically with the change in ethanolcontent. Up to an ethanol fraction of 30%, the speed of sound isinversely proportional to the ethanol fraction and above an ethanolfraction of 30%, the speed of sound is directly proportional to theethanol fraction.

Returning to FIG. 3, at 312, the fuel ethanol content may be estimateddirectly based on two or more of the damping coefficient α of pressurepulsations, fuel rail pressure pulsation frequency f, change in fuelrail pressure during a pump stroke δp, fuel rail temperature T, and fuelrail pressure p. As an example, if water content is insignificant,damping coefficient α, fuel rail pressure pulsation frequency f, andchange in fuel rail pressure during a pump stroke op are a function ofethanol volume fraction y, fuel rail temperature T, & fuel rail pressurep: α=

(y,T,p), f=

(y,T,p), and δp=

(y,T,p)

A relationship between the above mentioned variables is given by:

$\left\{ {\begin{bmatrix}y_{1} \\\vdots \\y_{N}\end{bmatrix},\begin{bmatrix}T_{1} \\\vdots \\T_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\left\{ {\begin{bmatrix}\alpha_{1} \\\vdots \\\alpha_{N}\end{bmatrix},\begin{bmatrix}f_{1} \\\vdots \\f_{N}\end{bmatrix},\begin{bmatrix}{\delta\; p_{1}} \\\vdots \\{\delta\; p_{N}}\end{bmatrix}} \right\}$where 1, 2, . . . N are the number of measurements (data points) of eachof the variables. Inverse mapping

⁻¹,

⁻¹ and

⁻¹ such that ŷ_(α)=

⁻¹(α,T,p), ŷ_(f)=

⁻¹(f,T,p) and ŷ_(δp)=

⁻¹(δp,T,p) may be used to estimate the ethanol volume fraction.

⁻¹,

⁻¹ and

⁻¹ may be determined from a fit (plot) or a look-up table.

In this way, the ethanol volume fraction (y) may be determined using therelationships (1), (2) or (3):

$\begin{matrix}{\left\{ {\begin{bmatrix}\alpha_{1} \\\vdots \\\alpha_{N}\end{bmatrix},\begin{bmatrix}T_{1} \\\vdots \\T_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\begin{bmatrix}{\hat{y}}_{\alpha 1} \\\vdots \\{\hat{y}}_{\alpha\; N}\end{bmatrix}} & (1) \\{\left\{ {\begin{bmatrix}f_{1} \\\vdots \\f_{N}\end{bmatrix},\begin{bmatrix}T_{1} \\\vdots \\T_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\begin{bmatrix}{\hat{y}}_{f\; 1} \\\vdots \\{\hat{y}}_{f\; N}\end{bmatrix}} & (2) \\{\left\{ {\begin{bmatrix}{\delta\; p_{1}} \\\vdots \\{\delta\; p_{N}}\end{bmatrix},\begin{bmatrix}T_{1} \\\vdots \\T_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\begin{bmatrix}{\hat{y}}_{\delta\; p\; 1} \\\vdots \\{\hat{y}}_{\delta\; p\; N}\end{bmatrix}} & (3)\end{matrix}$

If dependence on fuel rail pressure (p) is neglibible (such as less than2%), fuel rail pressure (p) may be dropped from the estimation and theethanol volume fraction may be estimated as a function of dampingcoefficient (α) and fuel rail temperature (T) or a function of fuel railpressure pulsation frequency (f) and and fuel rail temperature (T).Ethanol content (y) may be estimated as ŷ_(α), ŷ_(f) or ŷ_(δp), or aweighted average of ŷ_(α), ŷ_(f) and ŷ_(δp). Due to a non-monotonicbehavior, the inverse mapping may give two possible ethanol contents.For example, a speed of sound of 1160 m/s can either correspond to anethanol content of 9% or 90%. In this case, another parameter, e.g.damping coefficient, may be used to determine which of the two estimatesbased on the speed of sound is the correct one. For example, if theethanol content estimated based on the damping coefficient is 10%, the90% estimate may be ignored, and ethanol content may be estimated as aweighted average of 9% and 10%.

As another example, if water content is significant but not known,damping coefficient α, fuel rail pressure pulsation frequency f, andchange in fuel rail pressure during a pump stroke op are a function ofethanol volume fraction y, water volume fraction x, fuel railtemperature T, & fuel rail pressure p: α=

*(y, x, T, p), f=

*(y, x, T, p), and δp=

*(y, x, T, p)

A relationship between the above mentioned variables is given by:

$\left\{ {\begin{bmatrix}y_{1} \\\vdots \\y_{N}\end{bmatrix},\begin{bmatrix}x_{1} \\\vdots \\x_{N}\end{bmatrix},\begin{bmatrix}T_{1} \\\vdots \\T_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\left\{ {\begin{bmatrix}\alpha_{1} \\\vdots \\\alpha_{N}\end{bmatrix},\begin{bmatrix}f_{1} \\\vdots \\f_{N}\end{bmatrix},\begin{bmatrix}{\delta\; p_{1}} \\\vdots \\{\delta\; p_{N}}\end{bmatrix}} \right\}$

The ethanol volume fraction (y) may be determined using the inverserelationships (1*), (2*) or (3*):

$\begin{matrix}{\left\{ {\begin{bmatrix}\alpha_{1} \\\vdots \\\alpha_{N}\end{bmatrix},\begin{bmatrix}f_{1} \\\vdots \\f_{N}\end{bmatrix},\begin{bmatrix}T_{1} \\\vdots \\T_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\begin{bmatrix}{\hat{y}}_{{({\alpha,f})}1} \\\vdots \\{\hat{y}}_{{({\alpha,f})}\; N}\end{bmatrix}} & \left( 1^{*} \right) \\{\left\{ {\begin{bmatrix}f_{1} \\\vdots \\f_{N}\end{bmatrix},\begin{bmatrix}{\delta\; p_{1}} \\\vdots \\{\delta\; p_{N}}\end{bmatrix},\begin{bmatrix}T_{1} \\\vdots \\T_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\begin{bmatrix}{\hat{y}}_{{({f,{\delta\; p}})}\; 1} \\\vdots \\{\hat{y}}_{{({f,{\delta\; p}})}\; N}\end{bmatrix}} & \left( 2^{*} \right) \\{\left\{ {\begin{bmatrix}\alpha_{1} \\\vdots \\\alpha_{N}\end{bmatrix},\begin{bmatrix}{\delta\; p_{1}} \\\vdots \\{\delta\; p_{N}}\end{bmatrix},\begin{bmatrix}T_{1} \\\vdots \\T_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\begin{bmatrix}{\hat{y}}_{{({\alpha,{\delta\; p}})}\; 1} \\\vdots \\{\hat{y}}_{{({\alpha,{\delta\; p}})}\; N}\end{bmatrix}} & \left( 3^{*} \right)\end{matrix}$

In certain countries, flexible fuel that is dispensed to the vehiclefuel tank may include water. Also, ethanol in fuel may adsorb water overtime. At 313, water content in fuel (volume fraction) may be estimatedbased on the fuel rail temperature, the resonant frequency (f) ofpressure pulsations, the change in fuel rail pressure (δp), and thedamping coefficient (α) of pressure pulsations in the fuel rail asestimated after a fuel injection or a pump stroke. Fuel water contentmay be estimated as a function of the fuel rail temperature and two ofthe resonant frequency (f) of pressure pulsations, the change in fuelrail pressure (δp), and the damping coefficient (α) of pressurepulsations in the fuel rail. A weighted average of the estimates basedon different inverse relations (1*), (2*) and (3*) may be used toimprove accuracy of the estimated water content.

During conditions when fuel ethanol content is known (such asestimated), the fuel water content may be estimated as one of a firstfunction of resonant frequency (f) and fuel rail temperature, a secondfunction of change in fuel rail pressure (δp) in fuel and fuel railtemperature, and as a third function of damping coefficient (α) and fuelrail temperature.

In this way, in one example, the ethanol and water fractions may beestimated using mappings that are a function of two or more of the bulkmodulus, speed of sound and viscosity. In another example, directmappings relating two or more of δp, f, and α to ethanol and waterfractions may be used. When using direct mappings, computation of thebulk modulus, speed of sound and viscosity as intermediate variables maynot be carried.

At 314, engine operations may be adjusted based on the estimated fuelethanol content and/or estimated fuel water content. The adjusted engineoperating parameters may include adjusting an amount of injected fuel,spark timing, and/or fuel injection timing according to the detectedchanges in fuel composition.

For example, if the ethanol percentage increases, an octane level ishigher and a spark timing may be advanced due to a higher activationenergy of ethanol compared to gasoline which in turn increases theignition period (for ethanol). Also, as ethanol content increases, theoctane number increases as does cooling effect from DI injectors,therefore spark timing may be advanced from a borderline conditiontowards MBT timing in response to an increase in ethanol content. Asanother example, the amount of fuel injected on a cold start may beincreased in response to an increase in ethanol content such thatsufficient fuel is vaporized prior to start up the engine. As anotherexample, the amount (mass) of injected fuel may be increased in responseto increase in ethanol content due to ethanol's lower stoichiometricair-to-fuel ratio. Also, each fraction of fuel delivered via DI and PFImay be adjusted based on an increase in ethanol content.

For example, if the fuel water content increases, fuel burn rates maydecrease and the ignition period may increase and a spark timing may beadvanced to allow a longer ignition period. Also, as the water contentin fuel increases, the fraction of gasoline and/or ethanol in fuel maydecrease, therefore an amount of fuel injected may be increased byincreasing injection timing and injection pulse width to maintain adesired amount of combustible (gasoline and/or ethanol) components.Further, as the fuel water content increases, during cold starts, anamount of fuel injected may be increased to maintain a desired amount ofvaporized combustible components.

At 316, the routine includes determining if the fuel water content ishigher than a threshold level. The threshold level may be based on afuel water content at which a phase separation (between ethanol andwater) may occur, rendering the fuel ineffective for engine operation.The threshold may be pre-calibrated to be lower than the fuel waterlevel at which the fuel may become ineffective such that the fuel may beused up prior to the fuel degradation.

If it is determined that fuel water content is higher than the thresholdwater content, at 320, the operator may be notified via a dashboardindication that the fuel needs to be used up within a threshold time.The threshold time may be based on the fuel water content at which thefuel will become ineffective. In one example, the operator may refuel(add new fuel), such that the older fuel may be mixed with the newerfuel, thereby reducing the effects of the diluted fuel. If it isdetermined that fuel water content is lower than the threshold level, itmay be inferred that the fuel may be continued to be used for engineoperation. At 318, it may be indicated that the current fuel is suitablefor combustion.

The above mentioned method may be used to estimate the fuel ethanolcontent of fuel in the fuel rail (not in fuel tank). In one example, ifbetween refueling and ethanol content estimation, the fuel in the fuelrail is not used (such as injected to cylinders), there may be adifference in the ethanol content as estimated (based on fuel in fuelrail) relative to the ethanol content of fuel in the fuel tank. Themethod described in FIG. 16 may be used to estimate fuel ethanol contentin the fuel tank. Therefore, since the composition of the fuel beingdispensed by the port injectors might be different than the compositionof the fuel being dispensed by the direct injectors, some vehicles mayuse both methods as described in FIG. 3 and FIG. 16 for fuel ethanolestimation.

FIG. 4 shows an example method 400 that can be implemented to estimatean age of fuel such as gasoline in the fuel tank. Fuel age is anindication of the change in fuel constituents with time due tovaporization of the fuel's lighter more volatile ends. The fuel agingprocess is a function of duration and conditions at which the fuel isstored in the fuel tank. At 402, current vehicle and engine operatingparameters may be determined. The parameters may include vehicle speed,torque demand, engine speed, engine temperature, etc. The controller mayestimate a timing of fuel injection and an amount of fuel supplied tothe fuel injectors (direct injectors and/or port injectors) via thefirst fuel rail (such as first fuel rail 250 in FIG. 2) coupled to thedirect injectors (such as direct injectors 252 in FIG. 2) and the secondfuel rail (such as second fuel rail 260 in FIG. 2) coupled to the portinjectors (such as port injectors 262 in FIG. 2). The controller maymonitor operation of a fuel pump (such as high pressure pump 214 in FIG.2) such as timing of a fuel pump stroke.

At 404, the routine includes determining if conditions are met for fuelage determination. Fuel age determination may be carried out in anengine using gasoline as fuel. Thus, in some examples, the fuel agedetermination may be carried out only in vehicles configured to operatewith gasoline. In another example, fuel age estimation may be carriedout in vehicles configured to operate with flexible fuel (such ascontaining alcohol) if the alcohol content is known (such as based onethanol content fuel tank sensor and/or adaptation algorithms using theexhaust oxygen sensor).

The conditions may include the vehicle being propelled via engine torquewith fuel being supplied to the injectors via a fuel rail (such as thefirst fuel rail). The conditions may also include a first thresholdduration of vehicle operation with motor torque (fuel not combusting).For example, if the vehicle is operated for 7 days without engineoperation, a fuel age determination may be carried out at theimmediately subsequent engine start. Internal electronic control unitsoak times, connect vehicles (vehicle to vehicle, infrastructure tovehicle), and/or cell phones connected to the vehicle controller may beused to access dates and determine time elapsed since previous fuelusage. The conditions may further include a second threshold duration oftime elapsing since a prior fuel age estimation. For example, suchestimations may be carried out periodically after every 15 days. Also,the conditions may include a third threshold duration of time duringwhich less than a threshold quantity of fuel is consumed. If it isdetermined that conditions are not met for fuel age determination, at406, current engine operation may be continued without fuel agedetermination. Engine operation may include supplying fuel to one ormore fuel injectors via one or more fuel rails.

If it is determined that conditions are met for fuel age determination,at 408, fuel rail temperature may be estimated via a fuel railtemperature sensor (such as first fuel rail temperature sensor 232 inFIG. 2) coupled to the fuel rail. Alternatively, fuel rail temperaturemay be estimated using a physics-based or empirical model relating fuelrail temperature to the engine operating conditions and states.

At 410, one or more of a resonant frequency (f) of pressure pulsations,a change in fuel rail pressure (δp), and a damping coefficient (α) ofpressure pulsations in the fuel rail may be estimated after a fuelinjection or a pump stroke. Fuel bulk modulus may be estimated as afunction of the change in fuel rail pressure (δp) caused by a change inan amount of fuel in the fuel rail (such as at pump stroke or injectionevent), a speed of sound in fuel may be estimated as a function of theresonant frequency (f) of pressure pulsations in the fuel rail due tothe fuel pump stroke or the fuel injection, and the fuel viscosity maybe estimated as a function of the damping coefficient (α) of pressurepulsations in the fuel rail after the fuel pump stroke or the fuelinjection. Estimation of each of the resonant frequency (f) of pressurepulsations, the change in fuel rail pressure (δp), and the dampingcoefficient (α) of pressure pulsations in the fuel rail is discussed indetails in step 310 of FIG. 3 and is not reiterated.

At 412, fuel age may be estimated based on the fuel rail temperature andat least one of the resonant frequency (f) of pressure pulsations, thechange in fuel rail pressure (δp), and on the damping coefficient (α) ofpressure pulsations in the fuel rail as estimated after a fuel injectionor a pump stroke.

Due to fuel aging, a change in the concentration of the lighter ends(molecules with fewer Carbon atoms e.g. C₃ and C₄) and heavier ends mayoccur. As an example, fuel aging may cause an increase in theconcentration of the heavier ends and a decrease in the concentration ofthe lighter ends. Each of the fuel bulk modulus, the speed of sound infuel, and the fuel viscosity may be a function of the concentrations ofthe gasoline lighter and heavier ends (indicative of fuel age). Saidanother way, the fuel age may be estimated based on the fuel railtemperature and at least one of the estimated fuel bulk modulus, thespeed of sound in fuel, and the fuel viscosity.

In this way, the fuel ethanol content may be estimated as a firstfunction of the fuel rail temperature and two or more of the resonantfrequency of pressure pulsations, the change in fuel rail pressure, andthe damping coefficient of pressure pulsations, the fuel age may beestimated as a second function of the fuel rail temperature and one ormore of the resonant frequency of pressure pulsations, the change infuel rail pressure, and the damping coefficient of pressure pulsations,and the fuel water content may be estimated as a third function of thefuel rail temperature and two or more of the resonant frequency ofpressure pulsations, the change in fuel rail pressure, and the dampingcoefficient of pressure pulsations. While computing the first functionand the third function, it may be assumes that an effect of fuel agingis not significant and while computing the second function, it may beassumed that fuel ethanol content and fuel water content is either knownor not significant.

At 414, engine operations may be adjusted based on the estimated fuelage. The adjusted engine operating parameters may include amount of fuelinjected, spark timing, and fuel injection timing, according to thedetected changes in fuel composition. For example, an aged fuel may havea larger concentration of gasoline's heavier, less volatile ends and asa result, a larger amount of fuel may be injected during a cold start.As an example, fuel injection timing and injection pulse width may beadjusted based on fuel age and/or due to different vaporization rates ofthe constituents of the aged fuel. The fuel injection timing andinjection pulse width may be increased with an increase in fuel age. Asanother example, spark timing may be advanced to MBT to account forchanges in the ignition period due to fuel aging.

At 416, the routine includes determining if the fuel age is higher thana threshold age. The threshold age may be based on the increasedconcentration of the heavier ends at which the fuel may be ineffective.The threshold may be pre-calibrated to be lower than the fuel age atwhich the fuel may become ineffective such that the aging fuel may beused up prior to the fuel degradation.

If it is determined that fuel age is higher than the threshold age, at418, the operator may be notified via a dashboard indication that thefuel needs to be used up within a threshold time. The threshold time maybe based on the fuel age at which the fuel will become ineffective. Inone example, on a hybrid vehicle, the controller may increase the enginecontribution to the total demanded power to consume the remaining fuelbefore it becomes ineffective. In another example, the operator may alsorefuel (add new fuel), such that the older (aged) fuel may be diluted,thereby reducing the effects of aged fuel. If it is determined that fuelage is lower than the threshold age, it may be inferred that the fuelmay be continued to be used for engine operation. At 420, it may beindicated that the current fuel is suitable for combustion.

The above mentioned method may be used to estimate the fuel age of fuelin the fuel rail (not in fuel tank). In one example, if the vehicle isnot operated via engine torque (consuming fuel) for a prolongedduration, there may be a difference in the fuel age as estimated (basedon fuel in fuel rail) relative to the age of fuel in the fuel tank. Themethod described in FIG. 17 may be used to estimate fuel age in the fueltank. Therefore, since the fuel age of the fuel being dispensed by theport injectors might be different than the age of the fuel beingdispensed by the direct injectors, some vehicles may use both methods asdescribed in FIG. 4 and FIG. 17 for fuel age estimation.

In this way, during a first condition, a fuel rail temperature may beestimated, volume fractions of ethanol and water in fuel contained in afuel tank may be estimated based on an estimated fuel rail temperatureand two of an estimated fuel bulk modulus, an estimated fuel viscosity,and a speed of sound in fuel, engine operation may be adjusted based onthe estimated volume fraction of ethanol, and during a second condition,the fuel rail temperature may be estimated, an age of the fuel containedin the fuel tank may be estimated based on the estimated fuel railtemperature and one of the estimated fuel bulk modulus, the estimatedfuel viscosity, and the speed of sound in fuel, and engine operation maybe adjusted based on the age of the fuel. The first condition mayinclude completion of a refueling event, the fuel being a flexible fueland the second condition may include completion of a threshold distanceof travel and/or duration of travel since an immediately previous fuelage estimation, the fuel being gasoline.

FIG. 5 shows an example method 500 that can be implemented to estimate avolume fraction of ethanol in fuel and a fuel rail temperature. Unlikethe method for fuel ethanol content estimation described in FIG. 3, inthis method, fuel rail temperature is not used as an input forestimating the fuel ethanol content. At 502, current vehicle and engineoperating parameters may be determined. The determined parameters areelaborated in step 302 in FIG. 3 and not reiterated.

At 504, the routine includes determining if conditions are met for fuelethanol content determination. The conditions for ethanol volumefraction are elaborated in step 304 in FIG. 3 and not reiterated. If itis determined that conditions are not met for fuel ethanol contentdetermination, at 506, current engine operation may be continued withoutfuel ethanol content determination. Engine operation may includesupplying fuel to one or more fuel injectors via one or more fuel rails.

If it is determined that conditions are met for fuel ethanol contentdetermination, at 508, each of a resonant frequency (f) of pressurepulsations, a change in fuel rail pressure (δp), and a dampingcoefficient (α) of pressure pulsations in the fuel rail may be estimatedafter a fuel injection or a pump stroke. Estimation of each of theresonant frequency (f) of pressure pulsations, the change in fuel railpressure (δp), and the damping coefficient (α) of pressure pulsations inthe fuel rail is discussed in details in step 310 of FIG. 3 and is notreiterated. Fuel bulk modulus may be estimated as a function of thechange in fuel rail pressure (δp) caused by a change in an amount offuel in the fuel rail (such as at pump stroke or injection event), aspeed of sound in fuel may be estimated as a function of the resonantfrequency (f) of pressure pulsations in the fuel rail due to the fuelpump stroke or the fuel injection, and the fuel viscosity may beestimated as a function of the damping coefficient (α) of pressurepulsations in the fuel rail after the fuel pump stroke or the fuelinjection.

At 510, fuel ethanol content (volume fraction) may be estimated based onthe resonant frequency (f) of pressure pulsations, the change in fuelrail pressure (δp), and the damping coefficient (α) of pressurepulsations in the fuel rail as estimated after a fuel injection or apump stroke. During conditions when fuel water content is not known, thefuel ethanol content may be estimated as a function of each of theresonant frequency (f) of pressure pulsations, the change in fuel railpressure (δp), and the damping coefficient (α) of pressure pulsations inthe fuel rail. Said another way, the fuel ethanol content may beestimated based on each of the estimated fuel bulk modulus, the speed ofsound in fuel, and the fuel viscosity.

During conditions when fuel water content is known (or insignificant)fuel ethanol content may be estimated as a function of two of theresonant frequency (f) of pressure pulsations, the change in fuel railpressure (δp), and the damping coefficient (α) of pressure pulsations inthe fuel rail. Fuel ethanol content may be estimated directly based ontwo or more of the damping coefficient α of pressure pulsations, fuelrail pressure pulsation frequency f, change in fuel rail pressure duringa pump stroke δp, and fuel rail pressure p. As an example, dampingcoefficient α, fuel rail pressure pulsation frequency f, and change infuel rail pressure during a pump stroke δp are a functions of ethanolvolume fraction y, fuel rail temperature T, & fuel rail pressure p: α=

(y,T,p), f=

(y,T,p), and δp=

(y,T,p)

A relationship between the above mentioned variables is given by:

$\left\{ {\begin{bmatrix}y_{1} \\\vdots \\y_{N}\end{bmatrix},\begin{bmatrix}T_{1} \\\vdots \\T_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\left\{ {\begin{bmatrix}\alpha_{1} \\\vdots \\\alpha_{N}\end{bmatrix},\begin{bmatrix}f_{1} \\\vdots \\f_{N}\end{bmatrix},\begin{bmatrix}{\delta\; p_{1}} \\\vdots \\{\delta\; p_{N}}\end{bmatrix}} \right\}$where 1, 2, . . . N are the number of measurements (data points) of eachof the variables.

Inverse mapping l such that ŷ_(α,f)=l(α, f, p) may be used to estimatethe ethanol volume fraction without the knowledge of fuel railtemperature. l may be determined from a fit (plot) or a look-up table.

In this way, the ethanol volume fraction (y) may be determined using therelationship (4):

$\begin{matrix}{\left\{ {\begin{bmatrix}\alpha_{1} \\\vdots \\\alpha_{N}\end{bmatrix},\begin{bmatrix}f_{1} \\\vdots \\f_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\begin{bmatrix}{\hat{y}}_{1} \\\vdots \\{\hat{y}}_{\; N}\end{bmatrix}} & (4)\end{matrix}$

If dependence on fuel rail pressure (p) is negligible (such as less than2%), fuel rail pressure (p) may be dropped from the estimation and theethanol volume fraction may be estimated as a function of dampingcoefficient (α) and fuel rail pressure pulsation frequency (f). Otheralternative inverse mappings: ŷ_(α,δp)=l*(α,δp,p) or ŷ_(δp,f)=l**(δp, f,p) may be used. If dependence on fuel rail pressure (p) is negligible,fuel rail pressure (p) may also be dropped from the alternative inversemappings.

If fuel water content is significant and unknown, the dampingcoefficient α, fuel rail pressure pulsation frequency f, and change infuel rail pressure during a pump stroke op are a functions of ethanolvolume fraction y, water volume fraction x fuel rail temperature T, &fuel rail pressure p: α=

*(y, x, T, p), f=

*(y, x, T, p), and δp=

*(y, x, T, p). In this way, ethanol content is estimated using theinverse mapping ŷ=l***(α, f, δp, p).

In certain countries, flexible fuel that is dispensed to the vehiclefuel tank may include water. Also, ethanol in fuel may adsorb water overtime. At 511, water content in fuel (volume fraction) may be estimatedbased on each of the resonant frequency (f) of pressure pulsations, thechange in fuel rail pressure (δp), and on the damping coefficient (α) ofpressure pulsations in the fuel rail as estimated after a fuel injectionor a pump stroke.

At 512, fuel rail temperature may be estimated based on each of theresonant frequency (f) of pressure pulsations, the change in fuel railpressure (δp), and the damping coefficient (α) of pressure pulsations inthe fuel rail. Fuel rail temperature (T) may be estimated directly basedon two or more of the damping coefficient (α) of pressure pulsations,fuel rail pressure pulsation frequency (f), change in fuel rail pressureduring a pump stroke (δp), and fuel rail pressure (p). In one example,fuel water content is insignificant and fuel rail temperature (T) may bedetermined using the (inverse mapping) relationship (5):

$\begin{matrix}{\left\{ {\begin{bmatrix}\alpha_{1} \\\vdots \\\alpha_{N}\end{bmatrix},\begin{bmatrix}f_{1} \\\vdots \\f_{N}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\begin{bmatrix}{\hat{T}}_{1} \\\vdots \\{\hat{T}}_{\; N}\end{bmatrix}} & (5)\end{matrix}$

If dependence on fuel rail pressure (p) is negligible (such as less than2%), fuel rail pressure (p) may be dropped from the estimation and thefuel rail temperature may be estimated as a function of dampingcoefficient (α) and fuel rail pressure pulsation frequency (f). Inanother example, fuel water content is significant and unknown, and fuelrail temperature (T) may be determined using the (inverse mapping)relationship (5*):

$\begin{matrix}{\left\{ {\begin{bmatrix}\alpha_{1} \\\vdots \\\alpha_{N}\end{bmatrix},\begin{bmatrix}f_{1} \\\vdots \\f_{N}\end{bmatrix},\begin{bmatrix}{\delta\; p_{1}} \\\vdots \\{\delta\; p_{N}}\end{bmatrix},\begin{bmatrix}p_{1} \\\vdots \\p_{N}\end{bmatrix}} \right\}->\begin{bmatrix}{\hat{T}}_{1} \\\vdots \\{\hat{T}}_{\; N}\end{bmatrix}} & \left( 5^{*} \right)\end{matrix}$

Fueling may be adjusted based on the estimated fuel rail temperature.Since fuel volume is a function of pressure and temperature, injectorpulse width must be modified based on fuel rail temperature to inject atarget amount of fuel.

At 514, engine operations may be adjusted based on the estimated fuelethanol and water content. Example adjustments are elaborated in step314 in FIG. 3 and not reiterated. In this way, engine operation may beadjusted based on an estimated fuel ethanol content, the fuel ethanolcontent estimated based on two or more of fuel bulk modulus, fuelviscosity, and speed of sound in fuel.

At 516, the routine includes determining if the fuel water content ishigher than a threshold level. The threshold level may be based on afuel water content at which a phase separation (between ethanol andwater) may occur, rendering the fuel ineffective for engine operation.The threshold may be pre-calibrated to be lower than the fuel waterlevel at which the fuel may become ineffective such that the fuel may beused up prior to the fuel degradation.

If it is determined that fuel water content is higher than the thresholdwater content, at 520, the operator may be notified via a dashboardindication that the fuel needs to be used up within a threshold time.The threshold time may be based on the fuel water content at which thefuel will become ineffective. In one example, the operator may refuel(add new fuel), such that the older fuel may be mixed with the newerfuel, thereby reducing the effects of the diluted fuel. If it isdetermined that fuel water content is lower than the threshold level, itmay be inferred that the fuel may be continued to be used for engineoperation. At 518, it may be indicated that the current fuel is suitablefor combustion.

FIG. 6 shows an example method 600 that can be implemented to estimatean age of fuel in the fuel tank and a fuel rail temperature. Aspreviously described, fuel aging may cause an increase in theconcentration of the heavier ends and a decrease in the concentration ofthe lighter ends. Each of the fuel bulk modulus, the speed of sound infuel, and the fuel viscosity may be a function of the concentrations ofthe gasoline lighter and heavier ends (indicative of fuel age). Unlikethe method for fuel age estimation described in FIG. 4, in this method,fuel rail temperature is not used as an input for estimating fuel age.At 602, current vehicle and engine operating parameters may bedetermined. The parameters are elaborated in step 402 in FIG. 4 and notreiterated.

At 604, the routine includes determining if conditions are met for fuelage determination. The conditions are elaborated in step 404 in FIG. 4and not reiterated. If it is determined that conditions are not met forfuel age determination, at 606, current engine operation may becontinued without fuel age determination. Engine operation may includesupplying fuel to one or more fuel injectors via one or more fuel rails.

If it is determined that conditions are met for fuel age determination,at 608, two or more of a resonant frequency (f) of pressure pulsations,a change in fuel rail pressure (δp), and a damping coefficient (α) ofpressure pulsations in the fuel rail may be estimated after a fuelinjection or a pump stroke. Estimation of each of the resonant frequency(f) of pressure pulsations, the change in fuel rail pressure (δp), andthe damping coefficient (α) of pressure pulsations in the fuel rail isdiscussed in details in step 310 of FIG. 3 and is not reiterated. Fuelbulk modulus may be estimated as a function of the change in fuel railpressure (δp) caused by a change in an amount of fuel in the fuel rail(such as at pump stroke or injection event), a speed of sound in fuelmay be estimated as a function of the resonant frequency (f) of pressurepulsations in the fuel rail due to the fuel pump stroke or the fuelinjection, and the fuel viscosity may be estimated as a function of thedamping coefficient (α) of pressure pulsations in the fuel rail afterthe fuel pump stroke or the fuel injection.

At 610, fuel age may be estimated based on two or more of the resonantfrequency (f) of pressure pulsations, the change in fuel rail pressure(δp), and the damping coefficient (α) of pressure pulsations in the fuelrail. Fuel age, indicative of the concentrations of gasoline's lighterand heavier ends may be estimated as one of a function of resonantfrequency (f) and damping coefficient (α), a second function of changein fuel rail pressure (δp) in fuel and damping coefficient (α), and as athird function of damping coefficient (α) and resonant frequency (f). Aweighted average of the estimates from two or three of aforementionedfunctions may be used to improve accuracy. Said another way, the fuelage may be estimated based on at least two of the estimated fuel bulkmodulus, the speed of sound in fuel, and the fuel viscosity.

At 612, fuel rail temperature may be estimated as a function of at leasttwo of the resonant frequency (f) of pressure pulsations, the change infuel rail pressure (δp), and the damping coefficient (α) of pressurepulsations in the fuel rail.

At 614, engine operations may be adjusted based on the estimated fuelage. Example adjustments are elaborated in step 414 in FIG. 4 and notreiterated. At 616, the routine includes determining if the fuel age ishigher than a threshold age. The threshold age may be based on theincreased the concentration of the heavier ends at which the fuel may beineffective. The threshold may be pre-calibrated to be lower than thefuel age at which the fuel may become ineffective such that the agingfuel may be used up prior to the fuel degradation. If it is determinedthat fuel age is higher than the threshold age, at 620, the operator maybe notified via a dashboard indication that the fuel needs to be used upwithin a threshold time. In one example, on a hybrid vehicle, thecontroller may increase the engine contribution to the total demandedpower to consume the remaining fuel before it becomes ineffective. Inanother example, the operator may refuel (add new fuel), such that theolder (aged) fuel may be diluted, thereby reducing the effects of agedfuel. At 618, it may be indicated that the current fuel is suitable forcombustion and fuel change notification may not be provided.

In this way, during a first condition, a volume fractions of ethanol andwater in fuel contained in a fuel tank may be estimated based on (atleast) two of an estimated fuel bulk modulus, an estimated fuelviscosity, and a speed of sound in fuel, and engine operation may beadjusted based on the estimated volume fraction of ethanol, and during asecond condition, an age of the fuel contained in the fuel tank may beestimated based on (at least) two of the estimated fuel bulk modulus,the estimated fuel viscosity, and the speed of sound in fuel, and engineoperation may be adjusted based on the age of the fuel, and during eachof the first condition and the second condition, a fuel rail temperaturemay be estimated based on (at least) two of the estimated fuel bulkmodulus, the estimated fuel viscosity, and the speed of sound in fuel.The first condition may include completion of a refueling event, thefuel being a flexible fuel and the second condition may includecompletion of a threshold distance of travel and/or duration of travelsince an immediately previous fuel age estimation, the fuel beinggasoline.

FIG. 16 shows an example method 1600 that can be implemented to estimatea volume fraction of ethanol in a flexible-fuel containing ethanol. Incontrast to the method for fuel ethanol content estimation, as describedin FIG. 3, this method may be used to determine ethanol content of fuelin the fuel tank instead of the fuel rail. Since this method usessensors housed in the fuel tank for ethanol content estimation, thismethod may be used in systems that do not have direct injectors coupledto a fuel rail and/or may be carried out during engine operation whenfuel is being dispensed by port injectors.

At 1602, current vehicle and engine operating parameters may bedetermined. The parameters may include vehicle speed, torque demand,engine speed, engine temperature etc. The controller may estimate anamount of fuel supplied to the fuel injectors (such as the portinjectors 262 in FIG. 1) from a fuel tank.

At 1604, the routine includes determining if conditions are met for fuelethanol content determination. The conditions may include a refuelingevent. During refueling, fuel remaining in the fuel tank may mix withthe fuel that is being dispensed resulting in a fuel blend of existingand new fuel. The ethanol content of the fuel blend may be estimatedwithin a threshold duration (or a threshold distance of travel) afterthe refueling event. For example, such estimations may be carried outwithin 1 day of refueling or within 10 miles of travel after refueling.The conditions may further include a threshold duration of time elapsingsince a prior fuel ethanol content estimation. For example, suchestimations may be carried out periodically after every 15 days.

If it is determined that conditions are not met for fuel ethanol contentdetermination, at 606, current engine operation may be continued withoutfuel ethanol content determination. Engine operation may includesupplying fuel to one or more fuel injectors from the fuel tank. If itis determined that the conditions are met for fuel ethanol contentdetermination, at 1608, a fuel tank ultrasonic signal generator (such asultrasonic signal generator 240 in FIG. 2) coupled inside of a fuel tank(to a first fuel tank wall) may be activated. The ultrasonic signalgenerator may generate an ultrasonic signal which may travel from thefirst wall of the fuel tank (at which the generator is positioned) to anopposite, second, wall of the fuel tank through the fuel. The ultrasonicsignal generator may be reflected from the second wall of the tank andmay return to the first wall. The reflected ultrasonic signal may bereceived at an ultrasonic sensor (such as ultrasonic sensor 241 in FIG.2) coupled to the first wall, adjacent to the ultrasonic signalgenerator.

At 1610, a time of travel of the reflected ultrasonic signal from thesecond fuel tank wall may be estimated. As an example, upon firstgeneration of an ultrasonic signal by the generator located at the firstwall, a timer may be set, and upon return of the reflected ultrasonicsignal (from the second wall), as detected by the ultrasonic sensorcoupled proximal to the generator, the timer may be stopped. Theduration of time elapsed between the start and stop of the timer may bethe time of travel of the ultrasonic signal to and from the second wall.

At 1612, a speed of sound in fuel may be estimated based on theestimated time of travel. The distance between the first wall and thesecond wall may be retrieved from controller memory. The speed of soundin fuel may be estimated as a function of the distance between the firstwall and the second wall and the estimated time of travel of theultrasonic signal.

At 1616, an attenuation of ultrasonic signal in fuel may be estimated.As the ultrasonic signal travels through fuel, between the first walland the second wall, the signal may be attenuated. Said another way, theamplitude of the ultrasonic signal that is generated at the first wallmay be higher than the amplitude of the ultrasonic signal received atthe first wall after travelling back and forth through the fuel. Theultrasonic sensor may estimate a difference in amplitude between thegenerated ultrasonic signal and the reflected ultrasonic signal to inferthe attenuation co-efficient of the ultrasonic signal. The attenuationcoefficient may also be dependent on a material of the fuel tank. Thelevel of attenuation of the ultrasonic signal in fuel may vary based ona material of the fuel tank wall at which the signal is reflected. As anexample, certain materials (such as metals) may adsorb a part of thesignal when the signal is reflected from the wall. Also, the level ofattenuation may be based on a thickness of the wall from which thesignal is being reflected. The controller may use a look-up tablecalibrated based on the material and thickness of the fuel tank wall todetermine the attenuation co-efficient of the ultrasonic signal in fuelwith one or more of the difference in signal amplitude, the distancebetween the first wall and the second wall, and a time of travel ofultrasonic signal to and from the second wall as inputs, and theattenuation co-efficient as the output. The attenuation co-efficient maybe a function of fuel's viscosity and may be a based on the fuel ethanolcontent.

At 1618, temperature of fuel in the fuel tank may be estimated based oninputs from a fuel temperature sensor (such as temperature sensor 243 inFIG. 2) coupled to the fuel tank. At 1620, fuel ethanol content (volumefraction) may be estimated as a function of the speed of sound in fuel,temperature of fuel, and attenuation coefficient in fuel. Further, thefuel ethanol content may also be based on fuel pressure, however, fuelpressure may remain substantially constant during the measurement andamong different measurements.

At 1622, engine operations may be adjusted based on the estimated fuelethanol content. The adjusted engine operating parameters may includeamount of injected fuel, spark timing, and/or fuel injection timing,according to the current fuel ethanol content. For example, if theethanol percentage increases, a spark timing may be advanced due to ahigher activation energy of ethanol compared to gasoline and thus alonger ignition period for ethanol. As another example, the amount offuel injected on a cold start may be increased in response to anincrease in ethanol content such that sufficient fuel is vaporized tostart up the engine. As another example, the amount (mass) of injectedfuel may be increased in response to increase in ethanol content due toethanol's lower stoichiometric air-to-fuel ratio.

In this way, engine operation may be adjusted based on an estimated fuelethanol content, the fuel ethanol content estimated based on each of afuel temperature, a speed of sound in fuel, and an attenuationco-efficient of an ultrasonic signal in fuel.

FIG. 17 shows an example method 1700 that can be implemented to estimatean age of fuel in the fuel tank. In contrast to the method for fuel ageestimation, as described in FIG. 4, this method may be used to determineage of fuel in the fuel tank instead of the fuel rail. Since this methoduses sensors housed in the fuel tank for fuel age estimation, thismethod may be used in systems that do not have direct injectors coupledto a fuel rail and/or may be carried out during engine operation whenfuel is being dispensed by port injectors.

At 1702, current vehicle and engine operating parameters may bedetermined. The parameters may include vehicle speed, torque demand,engine speed, engine temperature etc. The controller may estimate anamount of fuel supplied to the fuel injectors (such as the portinjectors 262 in FIG. 1) from a fuel tank.

At 1704, the routine includes determining if conditions are met for fuelage determination. The conditions may include, a first thresholdduration of vehicle operation with motor torque (fuel not combusting).For example, if the vehicle is operated for 7 days without engineoperation, a fuel age determination may be carried out at theimmediately subsequent engine start. The conditions may further includea second threshold duration of time elapsing since a prior fuel ageestimation. For example, such estimations may be carried outperiodically after every 15 days. Also, the conditions may include athird threshold duration of time during which less than a thresholdquantity of fuel is consumed. If it is determined that conditions arenot met for fuel age determination, at 1706, current engine operationmay be continued without fuel age determination. Engine operation mayinclude supplying fuel to one or more fuel injectors via one or morefuel rails.

If it is determined that conditions are met for fuel age determination,at 1608, a fuel tank ultrasonic signal generator (such as ultrasonicsignal generator 240 in FIG. 2) coupled inside of a fuel tank (to afirst fuel tank wall) may be activated. The ultrasonic signal generatormay generate an ultrasonic signal which may travel from the first wallof the fuel tank (at which the generator is positioned) to an opposite,second, wall of the fuel tank through the fuel. The ultrasonic signalgenerator may be reflected from the second wall of the tank and mayreturn to the first wall. The reflected ultrasonic signal may bereceived at an ultrasonic sensor (such as ultrasonic sensor 241 in FIG.2) coupled to the first wall, adjacent to the ultrasonic signalgenerator.

At 1710, a time of travel of the reflected ultrasonic signal from thesecond fuel tank wall may be estimated. As an example, upon firstgeneration of an ultrasonic signal by the generator located at the firstwall, a timer may be set, and upon return of the reflected ultrasonicsignal (from the second wall), as detected by the ultrasonic sensorcoupled proximal to the generator, the timer may be stopped. Theduration of time elapsed between the start and stop of the timer may bethe time of travel of the ultrasonic signal to and from the second wall.

At 1712, a speed of sound in fuel may be estimated based on theestimated time of travel. The distance between the first wall and thesecond wall may be retrieved from controller memory. The speed of soundin fuel may be estimated as a function of the distance between the firstwall and the second wall and the estimated time of travel of theultrasonic signal.

At 1716, attenuation of ultrasonic signal in fuel may be estimated. Asthe ultrasonic signal travels through fuel, between the first wall andthe second wall, the signal may be attenuated. The ultrasonic sensor mayestimate a difference in amplitude between the generated ultrasonicsignal and the reflected ultrasonic signal to infer the attenuationco-efficient of the ultrasonic signal. The annotation constant may alsobe dependent on a material of the fuel tank. The level of attenuation ofthe ultrasonic signal in fuel may vary based on a material of the fueltank wall at which the signal is reflected. As an example, certainmaterials (such as metals) may adsorb a part of the signal when thesignal is reflected from the wall. Also, the level of attenuation may bebased on a thickness of the wall from which the signal is beingreflected. The controller may use a look-up table calibrated based onthe material and thickness of the fuel tank wall to determine theattenuation co-efficient of the ultrasonic signal in fuel with one ormore of the difference in signal amplitude, the distance between thefirst wall and the second wall, and a time of travel of ultrasonicsignal to and from the second wall as inputs, and the attenuationco-efficient as the output. The attenuation co-efficient may be afunction of the fuel's viscosity and may be a based on the fuel age.

At 1718, temperature of fuel in the fuel tank may be estimated based oninputs from a fuel temperature sensor (such as temperature sensor 243 inFIG. 2) coupled to the fuel tank. At 1720, fuel age, indicative of theconcentrations of gasoline's lighter and heavier ends, may be estimatedbased on each of the estimated speed of sound in fuel, attenuationco-efficient in fuel, and fuel temperature.

At 1722, engine operations may be adjusted based on the estimated fuelage. The adjusted engine operating parameters may include amount ofinjected fuel, spark timing, and/or fuel injection timing according tothe detected changes in fuel composition. For example, an aged fuel mayhave a larger concentration of gasoline's heavier, less volatile endsand as a result, a larger amount of fuel may be injected during a coldstart.

At 1724, the routine includes determining if the fuel age is higher thana threshold age. The threshold age may be based on the increased theconcentration of the heavier ends at which the fuel may be ineffective.The threshold may be pre-calibrated to be lower than the fuel age atwhich the fuel may become ineffective such that the aging fuel may beused up prior to the fuel degradation.

If it is determined that fuel age is higher than the threshold age, at1726, the operator may be notified via a dashboard indication that thefuel needs to be used up within a threshold time. The threshold time maybe based on the fuel age at which the fuel will become ineffective. Inone example, on a hybrid vehicle, the controller may increase the enginecontribution to the total demanded power to consume the remaining fuelbefore it becomes ineffective. In another example, the operator mayrefuel (add new fuel), such that the older (aged) fuel may be diluted,thereby reducing the effects of aged fuel. If it is determined that fuelage is lower than the threshold age, it may be inferred that the fuelmay be continued to be used for engine operation. At 1728, it may beindicated that the current fuel is suitable for combustion.

In this way, an ultrasonic signal may be generated via an ultrasonicsignal generator positioned on a first wall of a fuel tank, a reflectedultrasonic signal reflected from a second, opposite wall of the fueltank may be received, via an ultrasonic sensor, a speed of sound in fuelhoused in the fuel tank and an attenuation co-efficient of ultrasonicsignal in the fuel may be estimated based on the generated signal andthe reflected signal, a percentage of ethanol in the fuel or an age ofthe fuel may be estimated based on the estimated speed of sound in thefuel, the estimated attenuation co-efficient of ultrasonic signal in thefuel, and fuel temperature, and engine operation may be adjusted basedon the estimated percentage of ethanol in fuel or the age of the fuel.

FIG. 14 shows an example timeline 1400 illustrating determination offuel ethanol content in an alcohol containing fuel (flex-fuel) ingasoline using fuel rail pressure. In one example, fuel ethanol contentestimation may be carried out for vehicle engines such as a flex-fuelengine. The horizontal (x-axis) denotes time and the vertical markerst1-t4 identify significant times in the routine for fuel ethanol contentand fuel age determination.

The first plot, line 1402, shows a variation in fuel rail temperature asestimated via a fuel rail temperature sensor (such as temperature sensor232 in FIG. 2) coupled to the fuel rail (such as fuel rail 250 in FIG.2). The second plot, line 1404, shows a variation in fuel rail pressureas measured via a fuel rail pressure sensor (such as pressure sensor 248in FIG. 2) coupled to the fuel rail. The third plot, line 1406, showsfuel direct injection pulses. At each pulse, fuel is delivered from thefuel rail to the combustion chamber via the direct injectors (such asdirect injectors 252 in FIG. 2). The fourth plot, line 1410, shows arefueling event when fuel is dispensed to the fuel tank, via an externalnozzle, at a gas station. The fifth plot, line 1412, shows an ethanolcontent estimation event. The sixth plot, line 1416, shows spark timingrelative to maximum brake torque (MBT) timing.

Prior to time t1, fuel is injected via direct injection and the pump isoperated to transfer fuel from the fuel tank to the fuel rail forinjection. The fuel rail pressure fluctuates based on fuel injectionevents. The spark timing is adjusted based on engine operatingconditions. Fuel ethanol content is not carried out at this time. Attime t1, a fueling event is initiated and fuel is dispensed into thefuel tank from an external source. Between time t1 and t2, during thefueling event, as the vehicle is not being propelled, fuel is notinjected to the combustion chamber. As newly added fuel mixes with theexisting fuel in the fuel tank, the ethanol content of the mixed fuelmay change.

At time t2, fueling is completed and engine operation is resumed.Between time t2 and t3, fuel is pumped from the fuel tank to the fuelrail and fuel is injected to the combustion chambers via the fuelinjectors. At time t3, an ethanol content estimation is initiated and achange in the fuel rail pressure during a fuel injection is recorded.The change in fuel rail pressure is a difference in fuel rail pressurebefore and after the fuel injection. Each of a resonant frequency ofpressure pulsations in the fuel rail and a damping coefficient ofpressure pulsations in the fuel rail immediately after the fuelinjection are estimated. The fuel ethanol content is estimated as afunction of three or more of a fuel rail temperature, the change in fuelrail pressure, resonant frequency of pressure pulsations in the fuelrail, and the damping coefficient of pressure pulsations. Fuel ethanolcontent estimation is completed at time t4. As seen from the dashed line1413, after the ethanol content estimation, it is confirmed that thefuel ethanol content has increased after the fueling event (between timet1 and t2). Activation energy of ethanol is higher compared to gasolineand thus a higher ethanol content would require a longer ignitionperiod. Therefore, in response to the increased fuel ethanol content,after time t4, the engine is operated with spark timing advanced to MBT.Due to the advanced spark timing, engine efficiency is improved.

FIG. 15 shows an example timeline 1500 illustrating determination offuel age based on fuel rail pressure. The horizontal (x-axis) denotestime and the vertical markers t1-t3 identify significant times in theroutine for fuel age determination. In one example, fuel age estimationmay be carried out in vehicles using gasoline as fuel. In anotherexample, fuel age estimation may be carried out for a flex-fuel vehiclewherein the ethanol content of the fuel is known.

The first plot, line 1502, shows a variation in engine speed asestimated via a crankshaft sensor. The second plot, line 1504, showsfuel rail temperature as estimated via a fuel rail temperature sensor(such as temperature sensor 232 in FIG. 2) coupled to the fuel rail(such as fuel rail 250 in FIG. 2). The third plot, line 1506, shows avariation in fuel rail pressure as measured via a fuel rail pressuresensor (such as pressure sensor 248 in FIG. 2) coupled to the fuel rail.The fourth plot, line 1508, shows fuel direct injection pulses. At eachpulse, fuel is delivered from the fuel rail to the combustion chambervia the direct injectors (such as direct injectors 252 in FIG. 2). Thefifth plot, line 1510, shows a fuel age estimation event. Dashed line1511 shows an estimated fuel age. Dashed line 1512 shows a thresholdfuel age above which the operator is notified to use up the fuel. Thethreshold may be pre-calibrated to be lower than the fuel age at whichthe fuel may become ineffective such that the aging fuel may be used upprior to the fuel degradation. The sixth plot, line 1514, shows sparktiming relative to maximum brake torque (MBT) timing.

Prior to time t1, the engine is not operated as the vehicle is notpropelled via engine torque. Fuel injection and spark is disabled duringengine shut-down. At time t1, the engine is started from rest and fuelis injected to engine cylinders via direct injection. The fuel railpressure fluctuates based on fuel injection events. The spark timing isadjusted based on engine operating conditions. Fuel age estimation isnot carried out at this time.

At time t2, it is inferred that a threshold duration had elapsed sincethe previous fuel age determination. Therefore, at time t2, a fuel ageestimation is initiated. The fuel age is estimated as a function of twoor more of a fuel rail temperature, change in fuel rail pressure,resonant frequency of pressure pulsations in the fuel rail, and thedamping coefficient of pressure pulsations. Fuel age estimation iscompleted at time t3. After the fuel age estimation, it is confirmedthat the fuel age has increased. However, since the fuel age continuesto be below the threshold age 1512, the operator is not notified. Inresponse to the increased fuel age, after time t3, the engine isoperated with spark timing advanced to MBT. Due to the advanced sparktiming, engine efficiency is improved.

In this way, fuel ethanol content or fuel age may be estimated based onfuel rail pressure and then engine operation such as spark timing may beadjusted to improve fuel efficiency and engine performance.

FIG. 18 shows an example timeline 1800 illustrating determination offuel ethanol content based on ultrasonic signal. The horizontal (x-axis)denotes time and the vertical markers t1-t4 identify significant timesin the routine for fuel ethanol content determination.

The first plot, line 1802, shows a variation in fuel temperature asestimated via a fuel temperature sensor (such as temperature sensor 243in FIG. 2) coupled inside the fuel tank. The second plot, line 1804,shows generation of an ultrasonic signal from an ultrasonic signalgenerator (such as ultrasonic signal generator 240 in FIG. 2). Theultrasonic signal generator is coupled to a first wall of the fuel tank,and the generated ultrasonic signal gets reflected from a second,opposite wall of the fuel tank. The reflected ultrasonic signal isrecorded by an ultrasonic signal sensor (such as ultrasonic signalsensor 241 in FIG. 2) coupled to the first wall, proximal to theultrasonic signal generator. The third plot, line 1806, shows a fuelingevent when fuel is dispensed to the fuel tank, via an external nozzle,at a gas station. The fourth plot, line 1808, shows an ethanol contentestimation event. Dashed line 1809 shows an estimated fuel ethanolcontent during and after the ethanol content estimation event. The fifthplot, line 1812, shows spark timing relative to maximum brake torque(MBT) timing.

Prior to time t1, the vehicle is propelled by engine torque and thespark timing is maintained at MBT. Fuel temperature changes are based onengine operation and fuel is not supplied to the fuel tank. Fuel ethanolcontent or fuel age estimation is not carried out at this time and theultrasonic signal generator and sensor remain inactive. At time t1, afueling event is initiated and fuel is dispensed into the fuel tank.Between time t1 and t2, during the fueling event, as the vehicle is notbeing propelled and the engine is not operated. As newly added fuelmixes with the existing fuel in the fuel tank, the ethanol content ofthe mixed fuel may change.

At time t2, fueling is completed and engine operation is resumed.Between time t2 and t3, fuel is injected to the combustion chambers viathe fuel injectors. At time t3, ethanol content estimation of the fuelin the tank is initiated. In order to estimate the fuel ethanol content,the ultrasonic signal generator is activated to generate ultrasonicsignal. The ultrasonic signal, upon reflection from the opposite wall ofthe fuel tank is detected by the ultrasonic sensor. A speed of sound infuel is estimated based on a time of travel of the ultrasonic signalthrough the fuel, back and forth between a first wall of the fuel tankand a second, opposite, wall of the fuel tank, and a distance betweenthe first wall and the second wall. An attenuation coefficient of theultrasonic signal is estimated based on a change in amplitude of theultrasonic signal reaching the ultrasonic signal sensor after beingreflected from the second wall. The fuel ethanol content is estimatedbased on each of a fuel temperature, a speed of sound in the fuel, andan attenuation coefficient of ultrasonic signal in the fuel. Fuelethanol content estimation is completed at time t4. As seen from thedashed line 1809, after the ethanol content estimation, it is confirmedthat the fuel ethanol content has decreased after the fueling event(between time t1 and t2). Due to the ethanol content decreasing, betweentime t4 and t5, the spark timing is retarded MBT.

FIG. 19 shows an example timeline 1900 illustrating determination offuel age based on ultrasonic signal. The horizontal (x-axis) denotestime and the vertical markers t1-t3 identify significant times in theroutine for fuel age determination.

The first plot, line 1902, shows a variation in engine speed asestimated via a crankshaft sensor. The second plot, line 1904, shows avariation in fuel temperature as estimated via a fuel temperature sensor(such as temperature sensor 243 in FIG. 2) coupled inside the fuel tank.The third plot, line 1906, shows generation of an ultrasonic signal froman ultrasonic signal generator (such as ultrasonic signal generator 240in FIG. 2). The ultrasonic signal generator is coupled to a first wallof the fuel tank, and the generated ultrasonic signal gets reflectedfrom a second, opposite wall of the fuel tank. The reflected ultrasonicsignal is recorded by an ultrasonic signal sensor (such as ultrasonicsignal sensor 241 in FIG. 2) coupled to the first wall, proximal to theultrasonic signal generator. The fourth plot, line 1908, shows a fuelage estimation event. Dashed line 1909 shows an estimated fuel ageduring and after the fuel age estimation event. Dashed line 1910 showsthe threshold fuel age above which the operator is notified to changethe fuel. The fifth plot, line 1912, shows spark timing relative tomaximum brake torque (MBT) timing.

Prior to time t1, the engine is not operated as the vehicle is notpropelled via engine torque. Fuel injection and spark is disabled duringengine shut-down. At time t1, the engine is started from rest and fuelis injected to engine cylinders via direct injection. Fuel temperaturechanges are based on engine operation and fuel is not supplied to thefuel tank. Fuel age estimation is not carried out at this time and theultrasonic signal generator and sensor remain inactive.

At time t2, it is inferred that a threshold duration had elapsed sincethe previous fuel age determination. Therefore, at time t2, a fuel ageestimation is initiated. In order to estimate the fuel age, theultrasonic signal generator is activated to generate ultrasonic signal.The ultrasonic signal, upon reflection from the opposite wall of thefuel tank is detected by the ultrasonic sensor. A speed of sound in fuelis estimated based on a time of travel of the ultrasonic signal throughthe fuel, back and forth between a first wall of the fuel tank and asecond, opposite, wall of the fuel tank, and a distance between thefirst wall and the second wall. An attenuation coefficient of theultrasonic signal is estimated based on a change in amplitude of theultrasonic signal reaching the ultrasonic signal sensor after beingreflected from the second wall. Age of the fuel contained in the fueltank is estimated based on each of the fuel temperature, the speed ofsound in the fuel, and the attenuation coefficient of ultrasonic signalin the fuel. Fuel age estimation is completed at time t3.

After the fuel age estimation, it is confirmed that the fuel age hasincreased. However, since the fuel age continues to be below thethreshold age 1910, the operator is not notified. In response to theincreased fuel age, after time t3, the engine is operated with sparktiming advanced to MBT. Due to the advanced spark timing, engineefficiency is improved.

In this way, fuel ethanol content or fuel age may be estimated based onreflection of an ultrasonic signal inside a fuel tank and then engineoperation such as spark timing may be adjusted to improve fuelefficiency and engine performance.

An example method for an engine comprises: adjusting engine operationbased on an estimated fuel age, the fuel age estimated based on each ofa fuel temperature, a speed of sound in fuel, and an attenuationco-efficient of an ultrasonic signal in fuel. In any preceding example,further comprising, additionally or optionally, estimating a fuelethanol content based on each of the fuel temperature, the speed ofsound in fuel, and the attenuation co-efficient of an ultrasonic signalin fuel. In any or all of the preceding examples, additionally oroptionally, the fuel ethanol content is a percentage of ethanol in fuelcontained in a fuel tank of an engine fuel system and wherein the fuelage is a function of a duration of storage of fuel in the fuel tank, andtemperature and pressure of the fuel in the tank, the fuel ageindicating a change in fuel constitution due to vaporization of volatilecomponents of the fuel. In any or all of the preceding examples,additionally or optionally, the speed of sound in fuel is estimatedbased on a time of travel of an ultrasonic signal through the fuel, backand forth between a first wall of the fuel tank and a second, opposite,wall of the fuel tank, and a distance between the first wall and thesecond wall. In any or all of the preceding examples, additionally oroptionally, the ultrasonic signal is generated by an ultrasonic signalgenerator coupled to the first wall of the fuel tank and the ultrasonicsignal is detected by an ultrasonic signal sensor coupled to the firstwall, adjacent to the ultrasonic signal generator, and wherein the fueltemperature is estimated via a fuel temperature sensor housed inside thefuel tank. In any or all of the preceding examples, additionally oroptionally, the ultrasonic signal is generated by an ultrasonic signalgenerator coupled to the first wall of the fuel tank and the ultrasonicsignal is detected by an ultrasonic signal sensor coupled to the firstwall, adjacent to the ultrasonic signal generator, and wherein the fueltemperature is estimated via a fuel temperature sensor housed inside thefuel tank. In any or all of the preceding examples, additionally oroptionally, the attenuation co-efficient of the ultrasonic signal isestimated based on a change in amplitude of the ultrasonic signalreaching the ultrasonic signal sensor after being reflected from thesecond wall. In any or all of the preceding examples, additionally oroptionally, the fuel ethanol content is estimated periodically at leastwithin a first threshold distance of travel and/or duration of travelafter a refueling event and the fuel age is estimated periodically aftercompletion of a second threshold distance of travel and/or duration oftravel since an immediately previous fuel age estimation, the secondthreshold distance of travel and/or duration of travel being higher thanthe first threshold distance of travel and/or duration of travel. In anyor all of the preceding examples, additionally or optionally, adjustingengine operations include adjusting spark timing based on the estimatedfuel ethanol content and/or the fuel age, the spark timing advanced toMBT in response to an increase in fuel ethanol content and/or fuel age.In any or all of the preceding examples, additionally or optionally,adjusting engine operations further include adjusting an amount of fuelinjected during a cold-start based on the estimated fuel ethanol contentand/or fuel age, the amount of fuel injected during the cold-startincreased in response to the increase in fuel ethanol content and theincrease in fuel age. In any or all of the preceding examples, themethod further comprising, additionally or optionally, in response to anincrease in fuel age to above a threshold age, notifying an operator touse/change the fuel.

Another example engine method, comprises: during a first condition,estimating a volume fraction of ethanol in fuel contained in a fuel tankbased on each of a fuel temperature, a speed of sound in the fuel, andan attenuation co-efficient of ultrasonic signal in the fuel, andadjusting engine operation based on the estimated volume fraction ofethanol; during a second condition, estimating an age of the fuelcontained in the fuel tank based on each of the fuel temperature, thespeed of sound in the fuel, and the attenuation co-efficient ofultrasonic signal in the fuel, and adjusting engine operation based onthe age of the fuel. In any preceding example, additionally oroptionally, the first condition includes completion of a refuelingevent, and wherein the second condition includes completion of athreshold distance of travel and/or duration of travel since animmediately previous fuel age estimation. In any or all of the precedingexamples, additionally or optionally, the ultrasonic signal is generatedby an ultrasonic signal generator coupled to a first wall of a fueltank, and the ultrasonic signal is detected by an ultrasonic sensorcoupled to the first wall, adjacent to the ultrasonic signal generator,each of the ultrasonic signal generator and the ultrasonic sensor beingimmersed in fuel. In any or all of the preceding examples, additionallyor optionally, the speed of sound is estimated based on a time of travelof a reflected ultrasonic signal to and from a second wall, opposite tothe first wall, and a distance between the first wall and the secondwall. In any or all of the preceding examples, additionally oroptionally, the attenuation co-efficient of the ultrasonic signal isestimated based on a decrease in amplitude of the reflected ultrasonicsignal returning to the first wall. In any or all of the precedingexamples, additionally or optionally, the adjusting engine operationbased on the estimated volume fraction of ethanol includes one or moreof advancing spark timing to MBT in response to an increase in thevolume fraction, and increasing an amount of fuel injected duringcold-start in response to an increase in the volume fraction, andwherein the adjusting engine operation based on the age of the fuelincludes increasing the amount of fuel injected during cold-start inresponse to an increase in the age.

Yet another example engine system, comprises: a controller with computerreadable instructions stored on non-transitory memory that, whenexecuted, cause the controller to: generate an ultrasonic signal via anultrasonic signal generator positioned on a first wall of a fuel tank;receive a reflected ultrasonic signal reflected from a second, oppositewall of the fuel tank, via an ultrasonic sensor; estimate a speed ofsound in fuel housed in the fuel tank and an attenuation co-efficient ofultrasonic signal in the fuel based on the generated signal and thereflected signal; estimate a percentage of ethanol in the fuel and/or anage of the fuel based on the estimated speed of sound in the fuel, theestimated attenuation co-efficient of ultrasonic signal in the fuel, andfuel temperature; and adjust engine operation based on the estimatedpercentage of ethanol in fuel and/or the age of the fuel. In anypreceding example, additionally or optionally, the speed of sound infuel is based on a time interval between the generation of theultrasonic signal from the first wall and receipt of the reflectedsignal at the first wall, and a distance between the first wall and thesecond wall. In any or all of the preceding examples, additionally oroptionally, the attenuation co-efficient of ultrasonic signal in fuel isbased on a difference in amplitude between the generated ultrasonicsignal and the reflected ultrasonic signal. In any or all of thepreceding examples, additionally or optionally, adjusting engineoperation includes adjusting one or more of spark timing and fuelinjection based on the estimated percentage of ethanol in fuel and/orthe estimated fuel age.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

As used herein, the term “approximately” is construed to mean plus orminus five percent of the range unless otherwise specified.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for an engine, comprising:adjusting engine operation based on an estimated fuel age, the fuel ageestimated based on each of a fuel temperature, a speed of sound in fuel,and an attenuation co-efficient of an ultrasonic signal in fuel.
 2. Themethod of claim 1, further comprising, estimating a fuel ethanol contentbased on each of the fuel temperature, the speed of sound in fuel, andthe attenuation co-efficient of an ultrasonic signal in fuel.
 3. Themethod of claim 2, wherein the fuel ethanol content is a percentage ofethanol in fuel contained in a fuel tank of an engine fuel system andwherein the fuel age is a function of a duration of storage of fuel inthe fuel tank, and temperature and pressure of the fuel in the tank, thefuel age indicating a change in fuel constitution due to vaporization ofvolatile components of the fuel.
 4. The method of claim 3, wherein thespeed of sound in fuel is estimated based on a time of travel of anultrasonic signal through the fuel, back and forth between a first wallof the fuel tank and a second, opposite, wall of the fuel tank, and adistance between the first wall and the second wall.
 5. The method ofclaim 4, wherein the ultrasonic signal is generated by an ultrasonicsignal generator coupled to the first wall of the fuel tank and theultrasonic signal is detected by an ultrasonic signal sensor coupled tothe first wall, adjacent to the ultrasonic signal generator, and whereinthe fuel temperature is estimated via a fuel temperature sensor housedinside the fuel tank.
 6. The method of claim 4, wherein the attenuationco-efficient of the ultrasonic signal is estimated based on a change inamplitude of the ultrasonic signal reaching the ultrasonic signal sensorafter being reflected from the second wall.
 7. The method of claim 1,wherein the fuel ethanol content is estimated periodically at leastwithin a first threshold distance of travel and/or duration of travelafter a refueling event and the fuel age is estimated periodically aftercompletion of a second threshold distance of travel and/or duration oftravel since an immediately previous fuel age estimation, the secondthreshold distance of travel and/or duration of travel being higher thanthe first threshold distance of travel and/or duration of travel.
 8. Themethod of claim 1, wherein adjusting engine operations include adjustingspark timing based on the estimated fuel ethanol content and/or the fuelage, the spark timing advanced to MBT in response to an increase in fuelethanol content and/or fuel age.
 9. The method of claim 7, whereinadjusting engine operations further include adjusting an amount of fuelinjected during a cold-start based on the estimated fuel ethanol contentand/or fuel age, the amount of fuel injected during the cold-startincreased in response to the increase in fuel ethanol content and theincrease in fuel age.
 10. The method of claim 1, further comprising, inresponse to an increase in fuel age to above a threshold age, notifyingan operator to use/change the fuel.
 11. An engine method, comprising:during a first condition, estimating a volume fraction of ethanol infuel contained in a fuel tank based on each of a fuel temperature, aspeed of sound in the fuel, and an attenuation co-efficient ofultrasonic signal in the fuel, and adjusting engine operation based onthe estimated volume fraction of ethanol; during a second condition,estimating an age of the fuel contained in the fuel tank based on eachof the fuel temperature, the speed of sound in the fuel, and theattenuation co-efficient of ultrasonic signal in the fuel, and adjustingengine operation based on the age of the fuel.
 12. The method of claim11, wherein the first condition includes completion of a refuelingevent, and wherein the second condition includes completion of athreshold distance of travel and/or duration of travel since animmediately previous fuel age estimation.
 13. The method of claim 11,wherein the ultrasonic signal is generated by an ultrasonic signalgenerator coupled to a first wall of a fuel tank, and the ultrasonicsignal is detected by an ultrasonic sensor coupled to the first wall,adjacent to the ultrasonic signal generator, each of the ultrasonicsignal generator and the ultrasonic sensor being immersed in fuel. 14.The method of claim 13, wherein the speed of sound is estimated based ona time of travel of a reflected ultrasonic signal to and from a secondwall, opposite to the first wall, and a distance between the first walland the second wall.
 15. The method of claim 13, wherein the attenuationco-efficient of the ultrasonic signal is estimated based on a decreasein amplitude of the reflected ultrasonic signal returning to the firstwall.
 16. The method of claim 11, wherein the adjusting engine operationbased on the estimated volume fraction of ethanol includes one or moreof advancing spark timing to MBT in response to an increase in thevolume fraction, and increasing an amount of fuel injected duringcold-start in response to an increase in the volume fraction, andwherein the adjusting engine operation based on the age of the fuelincludes increasing the amount of fuel injected during cold-start inresponse to an increase in the age.
 17. An engine system, comprising: acontroller with computer readable instructions stored on non-transitorymemory that, when executed, cause the controller to: generate anultrasonic signal via an ultrasonic signal generator positioned on afirst wall of a fuel tank; receive a reflected ultrasonic signalreflected from a second, opposite wall of the fuel tank, via anultrasonic sensor; estimate a speed of sound in fuel housed in the fueltank and an attenuation co-efficient of ultrasonic signal in the fuelbased on the generated signal and the reflected signal; estimate apercentage of ethanol in the fuel and/or an age of the fuel based on theestimated speed of sound in the fuel, the estimated attenuationco-efficient of ultrasonic signal in the fuel, and fuel temperature; andadjust engine operation based on the estimated percentage of ethanol infuel and/or the age of the fuel.
 18. The system of claim 17, wherein thespeed of sound in fuel is based on a time interval between thegeneration of the ultrasonic signal from the first wall and receipt ofthe reflected signal at the first wall, and a distance between the firstwall and the second wall.
 19. The system of claim 17, wherein theattenuation co-efficient of ultrasonic signal in fuel is based on adifference in amplitude between the generated ultrasonic signal and thereflected ultrasonic signal.
 20. The system of claim 17, whereinadjusting engine operation includes adjusting one or more of sparktiming and fuel injection based on the estimated percentage of ethanolin fuel and/or the estimated fuel age.